Timber and Steel Frame Construction And Insulation – Design Guidance

Thermal bridging results in the loss of heat when it flows from one material through a less resistant path, and this becomes a potential problem where the floor meets the wall at different locations in a building.

Floor/Wall junction: There is a risk of thermal bridging at the floor/wall junction: If Ballytherm Insulation is being positioned in front of supports it should go fully to the floor.

Wall/Roof junction: Avoiding thermal bridging where the wall meets the roof can be approached by packing fitting Ballytherm Insulation between the rafters. This removes any space between the plate of the wall and the bottom of the roof insulation. See (Figure 39) for more on this approach.

Intermediate Floors: It is challenging to avoid some break in the insulation layer when dealing with intermediate floors but the approach of tightly fitting the insulation between the head of the wall and the edges of the floor can make a significant difference. Have a look at Figure 40 to see how this works.

Doors/Windows: At openings, fitting the insulation board tightly to horizontal and vertical facings, and lining reveals with 20mm Ballytherm boards is the approach to take.


Timber-frame buildings are very susceptible to moisture, if not controlled properly. It is important to take preventative measures to avoid damaging condensation and dampness developing in a structure.

Removing moisture at source: In developing a building plan, regard should be had to ensuring that sources of water vapour are addressed at the point the vapour itself is created, i.e. normally bathrooms and kitchens.

External moisture: In terms of external moisture sources, provide a vapour control layer (VCL) to act as a barrier to prevent moist air or dampness getting through to the inside of the structure from an external location.

Construction moisture: Work a method of dealing with construction moisture into your design. An insulation product with good resistance on the warm side, but poor resistance on the cold side will allow vapour traverse out into the atmosphere.

Plywood use: Typically, plywood may be located outside studs; this material has high resistance to water vapour and so can be problematic. As a result, consideration should be given to using material with lower resistance. Alternatively, a high performance layer of vapour control, or the siting of the plywood inside the studs, could be considered as a preventative approach.

Risk analysis: Carry out a condensation risk analysis for your project. Best practice guidance EN ISO 13788 should be referenced.

Tips on Thermal Performance

It is impossible to avoid using fixings during construction. However fixings such as wall ties etc. do have an impact on the performance of your thermal insulator layer. You can offset heat loss by careful choice of fixing, in terms of both materials and size. Stainless steel is one of the better options. Also, look for fixings which have a narrow size in terms of its cross section – this will minimize the area over which thermal losses can occur.

Heating appliances generally require to be fitted with a flue – which then of course has to penetrate the wall. Here you need to minimise contact between the hot pipe and the insulation. This is done by keeping a space between the insulating layer and the outlet, generally of 25mm in size, by using a protective cylindrical length of pipe. A combined type flue is another alternative you could look into.

figure 1

More Information:

For more information about Ballytherm insulation – the thermal insulator for timber–frame buildings  contact us at 0800 644 6900, email us at info@ballytherm.co.uk or use our contact form. One of our timber-frame insulation experts is ready to advise you now!