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Can I have a timber garage with a flat roof?


Can you have a timber garage with a flat roof? You can, but there may be better options. We’ll discuss the pros and cons and look at some alternatives.

Why choose a timber garage with a flat roof?

A Gillies and Mackay apex garage stained with Jacobean Walnut Sadolin.

Roof pitch contributes to a garage’s aesthetic appearance and its success at staying weatherproof. Most timber garages have either an apex roof, a pent roof or a flat roof. 

An apex roof has two sloping sides that meet in the middle to form a point. A pent roof has a single aspect higher at one side of the building than the other. A flat roof isn’t usually completely flat but has a slight slope to allow water to run off.

And water really is the thing when it comes to choosing your timber garage. Whatever the roof looks like it has to be able to keep rainwater out. Any areas on or around your garage that gather and retain water will cause problems in the long term.

What materials do flat garage roofs use?

A Gillies and Mackay pent garage painted pale grey. A classic car is parked in the garage.

But of course, many different types of buildings have flat roofs, including timber garages. Here are some of the roofing materials commonly used for flat roofs:

  • EDPM: EDPM is a synthetic rubber membrane. It’s fixed to the roof using adhesive to stick it on, ballast to hold it down, or mechanical fasteners to hold it in place. EDPM is an affordable material that’s generally reliable. However, variations in quality and installation methods can lead to problems like leaking, cracking and ponding, where water gathers at certain points on the roof.
  • Roofing felt: Bitumen-coated sheets of roofing material glued or nailed onto the roof. Once upon a time Gillies & Mackay used roofing felt, but it wasn’t a reliable material in the long term. We began phasing roofing felt out on pent sheds first because the lower-pitched roof meant that water could still sit on the felt. Given that roofing felt isn’t suitable for lower-pitched roofs, we wouldn’t recommend it for a flat roof.
  • Metal: There are various options for metal roofing, including corrugated and box profile sheets. Metal roofing is generally very reliable, but on flat roofs it is still prone to standing water. Because metal sheets are usually screwed on, any standing water around screws or screw holes can degrade these fixings over time, causing leaks. 

Other available roofing materials include PVC, silicon membranes and concrete fibre sheets. However, finding a roofing material that can withstand temperature changes, rainwater and degeneration over time is more difficult with a flat roof because of the potential for ponding.

Will having a flat roof on my garage make it easier to get planning permission?

Timber garages don’t always need planning permission. Depending on their size they may fall under permitted development rules. Our Planning Permission Checklist includes everything you need to help decide whether or not you have to apply. A responsible garage company will also be able to advise you.

To fall under permitted development rules, your garage must be under 4m tall. The height of the walls must be under 3m. This is pretty large for a garage, or any single-storey building. But as long as you can satisfy all of these conditions the roof style won’t affect your eligibility for permitted development. 

If your garage does need planning permission this permission might come with conditions. You can’t put an enormous pitched roof right in the middle of your neighbour’s view and block out all their natural light. There are situations where planning could specify a pent or flat-roofed garage, but these would be made very clear to you.

What problems does a timber garage with a flat roof have?

Flat roofs provide a large, well, flat surface for water to gather on. We’re low-key obsessed with water around here. When you build timber garden buildings, keeping water out is a primary objective. 

On an apex roof water easily runs off the roof and into gutters or onto the ground. Our pent Garages are designed with a pitch that allows easy water run-off. And even a roof that looks flat should have enough of a run to avoid water pooling on your garage roof.

Because standing water causes ALL the problems. The weight of the water can overload and damage the roof. Mould, algae and plant life will grow around standing water. Birds and other wildlife will come and drink it and bathe in it. Whatever your roofing material of choice, standing water will degrade it over time, potentially causing leaks and water damage. 

If your flat roof is installed properly on a level building with a perfectly level base, with an appropriate run, standing water shouldn’t be a problem. But timber garages are often susceptible to movement, especially if they’re not watertight. What started off as a flat building may not stay that way over time. 

How can I prevent movement in a timber garage?

While some degree of movement is always possible in a timber building, the main cause of excessive movement is water. The best way to prevent this excessive movement is to build a completely watertight timber garage. Gillies & Mackay Garages have a unique 3-Tier construction with an air cavity and breather membrane. If any moisture penetrates the outer layer of cladding, the inside of the building is protected by the cavity, the breather membrane and an OSB layer. We’re the only timber building company in Scotland that guarantees watertight garages. 

Can I have a timber garage with a flat roof?

A Gillies and Mackay pent garage paainted brown with Jacobean Walnut Sadolin. It has a grey Hormann garage door and there is a wooden gate fixed to its side.

Gillies & Mackay Garages don’t come with flat roofs. The potential problems that occur over time don’t fit with our ethos of creating timber garages built to last a lifetime. Opt for a pent roof or a pitched apex roof to reliably avoid standing water on your garage roof.

If you prefer a more modern aesthetic, our pent Garages provide the perfect solution for a lower-profile building that won’t suffer from standing water. Maintenance-free steel box profile roofing means that moss, algae and plant life won’t take root. Oh, and did I mention that our Garages don’t leak? So whether you’re storing a precious classic car, creating a watertight workspace or looking for some seriously secure storage, if you need a completely dry space, you need a Gillies & Mackay Garage.

If you’d like to see what these buildings look like, come and visit us at our Show Area here in Errol. There’s no substitute for seeing these mighty garages in person, and if you have any questions for us about your project, we’re more than happy to help.

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