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By Amy Hanlon on 15 Jan 2024

Should I insulate a timber garage?

Should you insulate a timber garage? Answering this question relies on one crucial factor: how your garage is constructed. 

The vast majority of timber garages on the market are made of a single layer or “skin” of timber. The boards that form the outside walls are also the boards that form the inside walls. A single-skinned garage is effectively a big shed. 

If your garage is single-skinned, insulating it is crucial. This not only improves the thermal efficiency of the building, making it cosier inside and more economical to heat, but it also helps prevent water ingress.

What is water ingress?

All single-skinned timber buildings are susceptible to water ingress. This happens when the moisture content in the air rises above 22%. At this point, moisture will soak into the walls of your garage and you’ll eventually find water inside the building. This doesn’t mean that your garage is leaking – it means that it’s seriously wet outside. 

Can I prevent water ingress in a garage?

There are several ways to minimise water ingress in single-skinned timber buildings. However, the important word here is minimise. Sometimes even the best-maintained single-skinned buildings still experience water ingress. Scotland sees a whole lot of water, after all! For the most part, water ingress won’t cause huge problems, but you should be aware that this can happen.

Will paint protect my garage from water ingress?

The best way to protect your garage is to paint the cladding with a good water-based paint. Make sure that any treatment you use is microporous to ensure that any water inside your garage can also get out. Timber buildings are designed to breathe – they let small amounts of moisture in and out of the building. We recommend Sadolin for painting a timber garage. You should repaint your building should every 3-5 years, or more if you experience particularly harsh weather. 

How does insulation prevent water ingress?

An insulated timber building is no longer single-skinned. The outside wall of timber cladding is exposed to the elements, and water may well penetrate this wall. But if you install insulation correctly this water is stopped in its tracks. How come? Because there’s an air cavity.

An air cavity is the most important feature if you want a watertight building. By leaving a small gap between the timber cladding and the insulation material, you create a water stop and add further insulation. Even if water does penetrate the outer cladding, this air gap prevents it from getting inside your building. 

You must ventilate your air gap to allow water out, and there are various ways to do this. But if you insulate your garage and add an air cavity, you’ll take care of any water ingress issues.

How much does it cost to insulate a timber garage?

There are some hard sums and probably a diagram or two involved to calculate exactly how much insulation and lining material you’ll need for your garage. 

But as a general estimate, it will cost roughly £100 per square metre of floor space to buy the materials for insulating and lining the walls, floor and roof of your garage. For example, if you have a 5m x 6m garage, insulation and lining materials will cost around £3000. 

This estimate is based on using 50mm foil-backed insulation board priced at around £23 per board and MDF lining priced around £55 per board. Both prices include VAT. It doesn’t include the cost of anti-fungal treatment, which is recommended for the inside of the timber cladding.

These figures are approximate and will vary depending on the exact dimensions of your garage. If you’re able to bulk-buy insulation and lining board you may be able to find it cheaper. You can also choose plasterboard or timber lining which will impact the cost.

Should I insulate a timber garage?

A diagram of the Gillies & Mackay timber garage specification.

Of course, there is another option. You can buy a garage that already has an air gap. If your garage is constructed this way, insulation becomes an optional addition. You’ll already have a cosy, watertight structure for storing a car or whatever else you want to put in there. 

Our timber garage specification was designed to combat water ingress and features a 22mm air gap as well as a layer of OSB for insulation and added stability. This 3-Tier structure will keep out the weather and is fully compliant with Building Standards. 

Timber garages have much thinner walls than brick or concrete garages but with the same energy efficiency. And if there’s a correctly installed air cavity, your building will keep the weather out

If you want to add insulation and lining to a Gillies & Mackay Garage you can – this is how we construct our Blackstone Garden Rooms. These are seriously sturdy buildings that are equivalent to a home extension in terms of their structural stability. 

If you’d like to check out our weathertight Garages and Garden Rooms, come and see them at our Show Area here in Errol. We’ll be on hand to answer any questions, and our Learning Centre has tons of information about our buildings.

Further reading:

Do I need planning permission to build a garage in Scotland?

How much does a medium timber garage cost?

How much does a garage base cost?

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