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.
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.
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.
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.
Advantages:
Disadvantages:
Advantages:
Disadvantages:
These diagrams show the principal structure of both options.
Construction detail – internally insulated log wall
Construction detail – externally insulated log wall
