How to insulate a garage conversion: Part 2 – Wall Insulation
In the first post in this series we looked at the building regulations that have to be complied with when carrying out a garage conversion including the U-values required and today we will be looking at wall insulation.
This is important as when you are converting a garage to be a more habitable room you need to make sure that the walls are properly insulated so you create a room which stays warm when it is needed. The U- values you need to achieve for walls are shown below:
U-Values for Extension of Existing Buildings in W/m2.K
*The first number applies where the existing building has U-values worse than 0.70 W/m.K in the walls and worse than 0.25 W/m.K in the ceiling.If the U-values are better than those figures the second number applies.
The existing construction of the garage wall will have an impact on the type and thickness of insulation chosen. Garages are usually built with a brick or block single skin solid wall, without any sort of insulation. Assuming that you are not going to tear down the walls and start from scratch, there are two methods of adding insulation to the garage wall; either to the inside (Internal Wall Insulation – IWI) or the outside of the wall (External Wall Insulation – EWI) and we will look at each of these in turn.
External Wall Insulation (EWI) on a garage conversion
Adding insulation, like Kingspan Kooltherm K5, to the exterior of the wall (under a suitable render system) is probably only suitable on a detached garage as adding the extra thickness of insulation and render to the outside of a garage that is attached to the side of the house may look odd, unless the entire house is being insulated and rendered in the same fashion. One advantage of adding the insulation to the exterior is that it maximises the amount of space within the room.
If space is limited and external wall insulation is the preferred solution then Optim-R vacuum insulated panels, a thinner solution, could be used to insulate the room to the standards required.
For more information on EWI solutions visit our website.
Internal Wall Insulation (IWI) on a garage conversion
The other, and probably more common, solution is to add the insulation to the inside of the garage. The simplest method of doing this is by using insulated plasterboard (like Kingspan K18 Insulated Plasterboard). These plasterboards are mechanically fixed to timber battens, at 600mm vertical centres, with either drywall screws at 300mm centres or large headed galvanised clout nails at 150mm centres. These fixings should allow for at least 22.5mm penetration of the timber. The timber battens should be protected by a strip of damp proof course, placed between the batten and the wall. Timber noggins should be positioned horizontally at floor and ceiling level and at a maximum of 1200mm vertical centres. This method provides insulation, plasterboard and a vapour control layer in one product.
If there is an impervious finish on the exterior of the wall, such as timber cladding or a waterproof render, which prevents moisture penetration then an insulated plasterboard (like Kingspan K17 Insulated Plasterboard) could be fixed to the wall using dot and dab method. We would recommend that an exposure risk analysis is carried out by our technical services department before using this method as this does not apply in some areas of the country.
The other option is to build a timber frame system with a breathable membrane and insulation (using insulation like Kingspan Kooltherm K12 framing board) between the studs and plasterboard. The plasterboard could be insulated plasterboard (K18) if extra thermal insulation is required. This method of insulating the garage wall is probably unnecessary unless the walls are too uneven to fix the plasterboard and need straightening out, although plastic shims can be used behind timber battens if only minor adjustments are needed. The full details of fixing this can be found in our quick guide.
Wall between house and garage
When you have a party wall between the garage and a heated space (such as the house) both sides of this wall will be heated spaces and no heat loss is assumed through this construction. There is no requirement for thermal insulation between two heated spaces.
Doors and Windows
When insulating around doors and windows you will need to put timber battens around the opening to support the board edges and fix the insulation to these battens. For the window reveals, we suggest screwing 25mm of Kooltherm K18 around the reveal to prevent cold bridging from happening within this area.
Next time we will be looking at how to insulate the roof, so check the construction of your garage roof ready for this. If you’ve missed the other posts on this topic they can be found below:
- How to insulate a garage conversion: Part 1 – Overview and Building Regulations/Standards
- How to insulate a garage conversion: Part 3 – Roof Insulation.
- How to insulate a garage conversion: Part 4 – Floor Insulation.
Share this blog post with your friends and colleagues by clicking on the social media icons below.