The self and custom build sector holds huge potential to diversify housing delivery and create more affordable, sustainable homes tailored to individual and community needs. However, access to the right kind of finance remains one of the biggest enablers and barriers to success.
At BMSL, the UK’s leading self-build mortgage specialist, we’ve spent over 26 years supporting over 30,000 individuals and families on their homebuilding journey. In this note, we set out how self-build mortgage products, particularly those offering guaranteed stage payments, are essential to unlocking affordability and managing risk in self and custom build.
What is a Self-Build Mortgage?
Unlike traditional mortgages, which release a single lump sum upon completion of a home, self-build mortgages release funds in stages throughout the construction process. This structure reflects how costs are incurred and helps manage cash flow as the build progresses. Each project has a bespoke cashflow however,
Typical Mortgage Stages Include:
Land purchase
Foundation and groundworks
Wall plate and roof (wind and watertight)
First and second fix (internal works)
Final completion
With most products, borrowers only pay interest on the funds drawn down, making this a cost-effective way to fund affordable housing projects.
Types of Stage Payment Mortgages
Guaranteed Stage Payments (Exclusive to BMSL)
BMSL has developed mortgage products with guaranteed stage payments, which release funds at pre-agreed points in the build, regardless of site value. This is essential for keeping projects on track, especially where affordability is key.
Two types of guaranteed payments:
Advance Stage Payments: Funds are paid before each stage ideal for covering deposits, ordering materials, when using offsite manufactured systems or meeting supplier terms.
Arrears Stage Payments: Funds are released after each stage, but the release is guaranteed, providing certainty that you will have the funds to pay your suppliers and contractors.
These options ensure that both low-deposit borrowers and those managing tight budgets can proceed with confidence and avoid costly delays.
Valuation-Based Stage Payments
Many self-build mortgages operate on an arrears stage payment basis, where funds are released after each build stage is completed and valued.
Key Issues:
Upfront Costs: You must fund each stage yourself before receiving any mortgage drawdown, creating cash flow pressure.
Valuation Delays: Funding relies on timely and favourable valuations. Any delays or shortfalls can disrupt the build.
Complex Projects: Renovations and conversions may not always match lender valuation models, complicating fund release.
Limited Accessibility: This model is less suited to first-time builders or those without access to significant upfront capital.
These challenges highlight the need to consider alternative models, such as advanced stage payments, which release funds earlier and ease cash flow constraints.
Matching Mortgage Models to Build Routes
Different self and custom-built routes present different financial needs:
·DIY / Self-Managed
Frequent funding is needed for trades and materials
· Custom Build
Funds must align with the developer or turnkey contract
BMSL matches each project’s unique build route and budget with the most suitable lender and mortgage product, including exclusive access to options requiring as little as 5% deposit on build costs.
Tips for Success in Affordable Self-Build
Start Early: Speak to BMSL before purchasing land to understand your borrowing power.
Budget Realistically: Always include professional fees, contingency (10–20%), and VAT where applicable.
Design to Budget: Work with your finance provider and designer from the outset to align your build with what you can afford.
Use a Specialist Broker: BMSL offers whole-of-market access and exclusive deals not available elsewhere.
Cashflow is Key: Choose a mortgage structure that reflects when costs are incurred, not just when value is added.
Common Pitfalls to Avoid
Underestimating upfront payment requirements for off-site or specialist systems
Omitting key costs (e.g. planning fees, warranties, site services)
Designing without a clear budget in place
Relying on traditional mortgages unsuited to phased construction
Choosing a lender unfamiliar with self or custom build
Why Buildstore Mortgage Services Limited?
BMSL is uniquely placed to support the self-build market, offering:
26+ years of specialist experience
Exclusive mortgage products with low deposits and guaranteed payments
Access to every lender in the market
Build costs assessment
Bespoke cashflow modelling for each project
Support for affordable, off-site, and custom-built routes
Whether it’s a first-time builder on a tight budget or a community-led project tackling housing need, BMSL provides the financial tools and expert guidance to make self and custom building viable, sustainable, and affordable.
Working with NACSBA and the Sector
BuildStore welcomes continued collaboration with NACSBA, local authorities, and sector stakeholders to:
Provide policy input on financing options
Support plot developers and enablers with finance-ready buyers
Educate consumers on affordable self-build finance
Strengthen the case for broader lender participation in the market
For more information or to explore partnership opportunities, please get in touch with our team.
BuildStore Mortgage Services The UK’s Self and Custom Build Mortgage Specialist
Nacsba Members Fleming Homes and Hugr Homes jumped on Mayflower Mortgage and Finance Self Builder Podcast to talk all things custom build earlier this week. The podcast explores the custom build journey and how both Fleming Homes and Hugr Homes work with their clients to create their dream homes. Mayflower explore the history of the companies and how they navigate the custom build process from concept to completion.
Eco credentials are becoming a given standard when designing a new home with more and more clients choosing an eco-home or zero-carbon approach to building their forever home. There are a number of factors to consider when designing these types of homes and the principles remain the same whether it’s an eco-home or zero carbon home. We talk to Kris Baxter of Studio 11 Architecture to hear his top tips on designing your eco home.
Zero Carbon Home Designed by Studio 11 Architecture in Lincolnshire
Fabric first
A fabric first approach is best described as putting a jacket around your home, in the form of insulation. Zero carbon homes require a super insulation to minimise heat loss and the commensurate carbon emissions. Another factor to consider would be how well your windows and doors perform thermally. Most houses now have significant amounts of glazing and it would be contradictory to have super insulated walls with poorly performing windows and doors.
At Studio 11 Architecture, we have an in-house team of Energy Assessors, meaning we are able to take a fabric first approach to designing your home from the concept stage, and can check how chosen materials will perform throughout the process.
The orientation of your home
When designing your home, your designer should look at the orientation of your home to consider “passive solar gains” made by glazing. If glazing is designed in your home with this in mind, you can achieve a building that gains heat during the day and stores it for use at night
Air tightness
One area where buildings can be significantly improved is air tightness. Heating air within a building and allowing it to escape increases the demand on the heating system which in turn burns more fossil fuels. By simply improving the air tightness, you can significantly reduce the heat loss of your home. To achieve good air tightness within a building you need to ensure good craftsmanship throughout the building and ensure all building elements are sealed appropriately. One thing to bear in mind is that it is possible for a building to be too air tight. Current building regulations require a minimum air permeability of buildings that are naturally ventilated and buildings below that threshold require mechanical ventilation.
Ventilation
Most buildings in the UK are designed to be naturally ventilated but when designing an eco or zero carbon home, there is usually an aspiration to achieve a very low air permeability. This means that some form of mechanical ventilation is required to prevent stagnation of air within the building and to provide its occupants with a constant supply of fresh air. The best approach for mechanical ventilation is a mechanical ventilation heat recovery system (MVHR) which provides fresh air the building but also uses a heat exchanger to remove the heat from the air exhausted from the building and transfers it to the fresh air coming into the building. This reduces heat loss whilst maintaining comfort levels within the building.
Eco Home Designed by Studio 11 Architecture In Essex
Heating and hot water systems
Most houses in the UK are provided with a gas or oil boiler, which heats water that in turns heat underfloor heating or radiators. Gas is a fossil fuel and therefore significant amounts of boilers producing emissions is detrimental to the environment. It is the government’s intention that by 2030 they will phase out gas connections to new houses. With that in mind, the construction industry has already started to look at alternatives and a good cost-effective alternative is the use of heat pumps, usually either ground source or air source, but can also be water source, depending on the site location. Heat pumps are similar to refrigeration units, but in reverse. They take heat from their source (air, ground or water) to heat water or air, which in turn heats the building. It is worth bearing in mind that heat pumps are powered by electricity and therefore are best for the environment when powered by electricity generated by a renewable source.
Electricity generation
Generating electricity on site is a great way of giving back to the environment, especially if you are able to generate more than you use. There are numerous ways to generate electricity, but the two most popular solutions are photovoltaic arrays and small-scale wind turbines. Both allow for the occupants of the building to use electricity generated on site and sell any surplus back to the national grid. To supplement the electricity generation, it may also be worth considering battery storage, which is especially useful if you have an electric vehicle where the electricity generated on site and stored in the battery could be used to charge your vehicle at home.
A- rated Self Build Home Designed by Studio 11 Architecture
Embodied Energy
Every material used in the construction of a building has embodied energy contained within it. Embodied energy being the energy required to manufacture or produce that building component together with the energy required to deliver and erect it. Commonly used building materials generally have a relatively high level of embodied energy. Examples of these would be concrete, brickwork, steel and plastics. The balance of designing a home with the longevity to offset the embodied energy created whilst considering the most environmentally friendly choice of material that may not last as long is a challenging process which requires a lot of thought and research.
Water Conservation
Depending upon where you live in the UK, the levels of rainfall will be different, however, it is always a good idea to minimise your water consumption. The three most common ways of doing this are incorporating rain water harvesting for use in watering the garden and washing cars, incorporating grey water harvesting for flushing toilets and finally, designing in sanitary ware which restricts water consumption. As a result, not only are you doing your bit for the environment, you are also making a significant annual saving financially
Ecology
General housing does not take into account ecology in any way and in many cases, by implementing even very small measures we can improve the ecology of a site significantly. These measures could take the form of bird boxes, insect habitats or simply putting aside some of your garden to serve as a wildflower meadow.
Zero Carbon Home designed by Studio 11 Architecture with future proofing for multiple generations in mind
Future-proofing your home
Our lives are forever changing, and if we wish to be truly eco in our approach to building our “forever home”, we need to make sure your home can adapt as your needs change. This can include making sure rooms can be multi-purpose and change use easily, your home is easily accessible and services such as electricity cables can be easily accessed and moved. It may even be worth considering your choice of frame so that walls can be changed within the structure relatively easily too.
Choosing glazing for your self-build project made easy with top tips from Kloeber.
Windows
Consider the design, style and frame material that would suit, think about how you plan to use the room and which way you want the windows to open and close. Bear in mind, from a planning perspective the council will take into consideration the choices you make, so speak to your architect for advice.
Bifold doors
Bifold doors can open up to 90% of the aperture so are ideal for smaller openings. We offer a variety of configurations with inward and outward opening options to suit your room. Create a cohesive living space with a level threshold and similar flooring inside and out.
Sliding doors
Sliding doors are ideal for larger apertures where the maximum opening will be round 70%. With slim sightlines and the option of wider panes of glass, you can have unbroken views of your garden all year round.
French doors
French doors are ideal if you want to add light to a room without opening up a large area to the outdoors. Suitable for a period or traditional style property, they can be used with glazing panels to create that bifold door look.
Types of glass
Consider whether you will need solar control glass for a south facing room or low iron glass for a north facing room. Try self-cleaning glass for areas you can’t reach or large expanses of glazing.
Energy efficiency
Choose doors and windows with a low U-value and consider double or triple glazing. Don’t forget to ask your supplier for thermal and weather-testing reports.
You can meet our team and see our products on our permanent stand 204 at The Festival of Sustainable Homes, 16-17 May, at the NSBRC, Swindon.
We also have showrooms in Cambridgeshire, West Sussex, Buckinghamshire, West London. Contact our friendly team on 01487 740044 or info@kloeber.co.uk to book your appointment today!
No matter how thick the walls of a log cabin home are, on its own, a log wall won’t meet UK building regulations if you’re using your log building to live in.
(Of course, if your log building is going to be used as a garage or a workshop, then log walls themselves will usually be sufficient – our thinnest logs start at a robust 70mm thick and will definitely still be warmer than your average shed!)
You’ll therefore need to insulate your log home. With the structural log walls of your log home kit, we provide a full, carefully designed frame to take the necessary insulation (note that for residential purposes this is typically at least 200mm thick, but we’ll design it to suit your requirements). We’ll also work with you to plan how you want to insulate the roof and floor of your home.
So what is the best way to insulate your log home? There are several things you’ll need to consider.
How much insulation do you need?
The thickness of insulation you will need depends on both the type of insulation you want to use, and the energy efficiency level that you need to achieve. The latter is defined by the current Building Regulations. In England and Wales, the relevant ‘Approved Document – Part L – Conservation of Fuel and Power’ is here, and for Scotland it is in Section 6 of the Building Standards Technical Handbook.
Of course you may choose to exceed the ‘backstop’ values in order to minimise energy bills, and you might even be aiming to reach Passivhaus standards. As an example, this case study illustrates how a well insulated home can also have very low running costs!
The unit that is used to measure how effective the various elements (walls, floor and roof) are at minimising the transmission of heat from the inside to the outside of the house (and of course vice versa in summer!), is called a ‘U-value’, and it is measured in watts per square metre per kelvin, or W/(m²K).
The lower the U-value, the more slowly heat can be transmitted through it, so the better the insulation performance. You can find a useful resource explaining U-values further here.
You’ll need to plan the insulation that you want to use in the floor, external walls, roof, and in the mid-floor (if your design has an upstairs), and within any partition walls between rooms – though this is for acoustic insulation purposes rather than energy efficiency.
What is the best type of insulation to use?
You need to decide what type of insulation you want to use – we can advise on the various options but ultimately the decision is yours. Insulation can be made from all kinds of materials, and they all have pros and cons.
Solid insulation sheets, typically made from polyisocyanurate (PIR), polyurethane rigid foam (PUR) or phenolic foam, tend to be highly energy efficient, and are often seen as the ‘best’ way to insulate any building.
Expanded polystyrene (EPS) and extruded polystyrene (XPS) sheets can also be used for insulation, but these are more commonly used for floor insulation (e.g. as part of an insulated raft foundation system). We plan to provide more information on foundation and floor insulation options in another Advice Centre article.
Solid insulation sheets have very good insulation values for the thickness of material, so would minimise the wall thickness needed for a given level of energy efficiency. They can also act as a vapour barrier, and can be used to reduce ‘cold bridging’ if used across the insulation framework as well. However, there are some drawbacks – first of all they need to be carefully cut to fit into the spaces in the insulation framework, so that air (and heat!) can’t get round the sides. It can also gradually give off the gas inside the insulation over time, which can make it shrink (see a discussion on the Green Building Forum here).
You can source flexible expanding tape to help secure it but that then adds another step into the process.
Another consideration with solid insulation sheets is that they are not all that acoustically efficient – you may find that there is more sound transmission from the outside or between rooms.
You may prefer to consider natural insulation such as sheep’s wool, hemp, or wood fibre. These all tend to come in batts / boards or rolls, usually sized to fit between the battens of the insulation framework, and are flexible so can be made to fit securely in place. You will usually need to have a thicker amount of insulation to achieve the same level of energy efficiency. These perform well acoustically; IndiNature’s IndiSilence hemp insulation partition roll and block are Quiet Mark certified. These materials also lock up carbon, boosting their eco-credentials.
Wood fibre board is quite a dense material, providing good insulation value but also having extra benefits by holding onto heat for longer. Combined with the solid log wall this can boost the thermal mass of the building. Heat is then released slowly into the building, evening out temperature changes. Have a look at this supplier document for more information.
Glass or mineral (rock) wool is another form of flexible insulation, which provides a good level of energy efficiency. Glass wool can be very itchy to install, and even mineral wool insulation can be quite dusty to use. For both of these products, it is a very good idea to wear disposable gloves, overalls and a mask over your nose. Three of Rockwool’s mineral wool products are also Quiet Mark approved – if you visit their stand at the NSBRC in Swindon you can experience this!
Yet another format of insulation would be a blown or loose fill insulation typically made from recycled paper, wood fibres, or mineral wool. Again these are likely to require a thicker level of insulation to achieve target U values. They can be suitable for both wall and roof insulation.
Where do I put the insulation? Inside or outside?
With our lovely log home kits you have the flexibility as to where the specially designed insulation framework is installed.
Assuming that your local planning authority has accepted a log building, you will probably want to install the insulation on the inside of the house. This is the most common choice. However, there can be situations where you might want to have the log structure as the interior structure of the house, with insulation outside, and then an external finish. Let’s have a look at the pros and cons of each option.
Internal insulation frame
Advantages:
Allows you to hide wiring behind internal cladding.
Gives you a choice of internal finishes on any wall (timber panelling, plasterboard, etc.)
The shell of the building can be constructed rapidly, with all internal work then being in the dry.
Disadvantages:
External finish will be horizontal logs.
External insulation frame
Advantages:
Allows the exterior to be finished with a range of alternative options, e.g. vertical timber cladding, horizontal timber cladding, render, brick slips etc.
An air gap between any rain shield cladding and the main structure can be easily included which some building control officers will insist on.
Solid log walls are good at moderating moisture levels inside the house and therefore provide good indoor air quality. You may therefore not need a vapour membrane.
Disadvantages:
Having solid log walls on the inside means that you have to plan very carefully for where any ducting / wiring / cabling is going to be installed. Holes will be drilled in the factory for wiring to be inserted during the build.
These diagrams show the principal structure of both options.
Construction detail – internally insulated log wall
Construction detail – externally insulated log wall
Q1 I’m planning to build an eco-friendly house but have concerns around the available living space with it being a small plot of land. Is a basement plantroom an option for me?
“Modern eco-homes require more than just insulation and solar panels. Advanced systems like PV, heat pumps, and air ventilation units are essential, but they need extra room to operate efficiently. These systems can quickly take up more space than traditional boilers and radiators, and without proper planning, you could end up sacrificing living space to accommodate them.
A dedicated plant room in your basement can house all your environmental systems keeping your heating, cooling, and ventilation equipment out of sight without taking away from your living area.
In addition, a plant room doesn’t need natural light, so you’re free to use it for everything from storing coats and shoes to even adding a laundry room. All the while, your main living space remains open, clutter-free, and sustainable.”
If this is something at the back of your mind as you’re planning your self build project, why not reach out to the specialists.
Q2 I would like to include a basement for extra living space in my self-build project, but I’m concerned about the amount of natural light I’ll be able to direct into the space. What options do I have?
“Naturally, when we think of basements, we don’t consider windows as a viable option for natural light to gain access. If the basement walls are exposed in any area around the property, it could be suitable to include a window to achieve this but depending on the topography of the land this may not be a viable option.
If windows are viable, it is always important to consider the size and placement of the window to ensure maximum exposure to natural light in addition to the material used to ensure no heat escapes.
Another solution would be the proper placement of light wells directing light from optimally sun exposed areas into the basement to create a naturally viable living space.”
Here are some success stories where natural light was an important consideration.
Q3 I’m planning to build my own house which includes a basement. I’m concerned that the project management is going to be unworkable and stressful considering the complexity of a basement build. I’d like to find a reliable basement contractor who can deliver on time with little stress whilst supporting me through the process. Can you help?
“Yes of course, we can do better than that.
At a fixed cost, Glatthaar deliver a full service from demolition of your existing property through groundworks and pilings to engineering and building your basement. We will hand over your site ready for the ground floor and beyond to be built on top without the complexity and stress of managing multiple contractors at one time. Furthermore, our AquaSafe® technology comes with a 10-year insurance backed warranty against water ingress giving you piece of mind beyond the completion of your project.” Glatthaar Keller ltd is also covered with PI insurance.
If this if this is a concern at the back of your mind as you’re moving forward with your project, why not reach out for a free consultation: https://www.glatthaar.co.uk/contact/
Q4 I have purchased some land in an area with a high water table, I’d like to build a basement but feel flooding will be a problem. Would you advise not building a basement in these conditions?
“We have built over 65,000 basements across Europe many in waterlogged areas. Due to our experience and continuous innovation we’re the UK’s only basement construction company that offer a full 10-year warranty against water ingress. Using our patented waterproof Aquasafe basement system we constructed a 313-tonne floating building basement which can be visited in our Schramberg facility in Germany.”
Q5 I‘m in the early stages of planning a new build home for me and my family. I would like a basement but have concerns about additional costs further down the line. What should I consider?
This is often the first conversation I have with a client and a typical early-stage concern. With each basement being unique, my first job with any project is to understand the scope of work.
The first step is to collect the correct information including the basement design and soil report along with the site map to understand where and how we need to support the ground to conduct our work. Often neighbouring properties must be supported by pilings which also offer support our plant equipment during construction. Depending on the results from the soil report pilings may also be needed to support the foundations of the basement and above ground structure.
This all sounds daunting which is why we offer a fixed cost including demolition of your old property through to the completion of your basement. We will guide you through the process leaning on our 45 years of experience building basements. Further, there is no obligation by getting a full quotation from us. The only cost to consider is the soil report which is needed for the foundations of your property with or without our services.
“The planning permission process is no different from a build without a basement, however, it would be an idea to reach out with your ideas for guidance on what is possible. For example, with our type A/B tanking system (external) we do need room around the basement to apply the waterproofing once it is in situ. This means that we may need to bring the walls in slightly on the basement to ensure we do not encroach on neighbouring properties when conducting our work. This is something you should consider during the design of the building.”
“Yes, the soil survey helps us understand the ground we are building the basement in it is important to understand how we need to engineer your basement to prevent subsidence and hydro lift. Also, it will allow us to plan the construction of the build effectively. The results of the soil survey are something we must and always pay attention to. That being said, it is not to understand if a basement can be built, it just dictates how we go about it.”
Our partners Land Science provide a great service to our customers with a basement specific package. You can contact them here: www.landscience.co.uk or you can order the soil survey directly by Glatthaar Keller Ltd.
Q8 My building plot is not flat, what are my options?
“There are many options for you that would come to light through a consultation. It is likely that more opportunities are open to you regarding external access to your basement or even integrating the basement into the land scaping of your garden. There may also be opportunities to bring more natural light into the basement. I see this as an opportunity rather than a problem.“
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