A flat garage roof has a way of making its owner wonder about a pitched one. The felt has split again, the ceiling stain has come back, and the neighbour's garage down the road has a smart tiled gable that looks as if it will never leak. Converting is possible, and for the right garage it is a good move. It is also a bigger project than replacing a covering. It involves new timbers, a different weight on the walls, a new look from the street and, usually, questions for the council. This guide helps you decide whether a pitched garage roof is the right answer, and explains what the work involves if it is.
Why people convert
There are four common reasons. The first is leaks. A flat roof has little margin for error, because water has barely any slope to leave by, while a pitched roof carries it off quickly. The second is appearance: a pitched roof matches the main house, particularly on an attached garage under the same eaves line, and can add real kerb appeal. The third is space. The roof void above a pitched garage gives storage, and with enough height it can become a room later. The fourth is lifespan. A tiled or slated roof, kept in good order, can outlast a flat covering by a wide margin, so the higher first cost is spread over a long time.
None of those reasons is a certain win. If your only problem is a failed covering on a sound deck, a new EPDM or GRP roof costs much less and solves the leak. Our guide to garage roof repair or replacement will help you check whether the roof you have can simply be re-covered.
What a pitched roof needs from the garage
A flat roof sits on the walls as a light, level lid. A pitched roof is a heavier, three-dimensional frame, and the walls have to carry and resist it. Four things decide whether the garage is suitable.
- The walls. Brick or block walls of sound construction can usually carry a new roof, with a wall plate (a timber bedded on top of the wall) to spread the load. Thin single-leaf walls, old sectional concrete panels, or walls that are cracked or bowed may need work first.
- The span. A single garage spans about the width of a car and a bit, and trussed rafters, factory-made triangular frames, work well. A double garage spans further and may need deeper timbers or a steel beam.
- The side walls. A pitched roof pushes outward as well as down. Trusses are tied at the base to prevent spreading, and the gable ends need restraint straps.
- The attachment to the house. If the garage adjoins the house, the new roof must tie into the house wall with a proper abutment and flashings.
Garages built with prefabricated concrete sections are a special case: the thin panels and posts were not designed for a heavy frame. Our guide to re-roofing concrete sectional garages explains what to check there.
How the conversion is built
The old flat roof is stripped back to the wall tops. Any asbestos cement sheeting is dealt with first, according to the rules covered in our guide to asbestos garage roof removal. A wall plate is fixed along each side wall using straps and bedding mortar, level and straight. The trusses, or cut rafters and a ridge board, are lifted into position at regular spacing and braced against each other. The gable ends are built up with brick, block or timber framing.
On top of the frame, the roof is covered in layers. A breathable underlay is laid over the rafters, the battens are fixed to the correct gauge for the tile or slate, and the covering goes on from the eaves upward. Ridge and verge pieces are fixed mechanically, in line with BS 5534, which does not rely on mortar alone. Fascia boards, soffits and gutters finish the eaves, and flashings seal against any adjoining wall. Underneath, the ceiling is either left at the old level, a boarded, insulated lid, or opened up into the roof space.
Choosing the covering
Once the frame is up, you can use almost any roofing material, which is part of the attraction. Concrete tiles are the common choice for budget and weight. Clay tiles and natural slate look better and last longer, at higher cost, and a lighter frame can carry man-made slate. Metal sheets, either profiled or standing seam, suit a modern building. At low pitches, tiles must be rated for them, since a tile that works at 40 degrees leaks at 20. We choose the pitch and the covering together, because they depend on each other.
Weight is a legal as well as a physical question. A covering that is far heavier than what it replaces is something building control wants to check, since the structure has to carry it. A new frame is designed for its load, but the walls and foundations below should be sound. If you want to see what other garage coverings are available and how they compare, our guide to garage roof options sets them side by side.
Ventilation, insulation and the roof void
A pitched garage roof traps a pocket of air under the covering, and that air has to move. Without ventilation, warm damp air from the garage condenses on the cold underside of the underlay and drips onto stored items. The usual remedy is to ventilate at the eaves and the ridge, with a continuous slot or vents in the soffit and a vent at the top, so a gentle draught runs through the void. Breathable underlay lets some moisture pass through, but it does not replace ventilation.
Whether to insulate depends on how the garage is used. A store for bikes and tools needs no insulation. A workshop, or a garage you may convert, justifies insulation laid between and over the ceiling joists, kept clear of the eaves ventilation. If a future conversion is possible, ask the roofer to size the trusses and the loft hatch for it now, since changing them later is expensive.
Disruption and timing
Converting the roof of a garage is a mess while it lasts. The old covering comes off, the garage is exposed to weather until the new roof is felted, and anything stored inside needs protecting or moving. We plan the stages so the building is open for as short a time as we can manage, with the frame and underlay going on in quick succession, and the roof is made weathertight each evening where the job spans more than a day. A calm spell helps, as lifting trusses in strong wind is unsafe. Scaffold goes up before the old roof is touched, and the tiles are loaded onto it, so ladders are not carrying them.
Planning, building control and neighbours
A pitched roof raises the height of the building, and on a garage close to a boundary that can matter. Outbuildings and garages are subject to rules on height, eaves and distance from the boundary, which are different for attached and detached buildings and tighter in conservation areas, and for listed properties. We cannot give legal advice, so put the question to the planning team at your council before you start, and ask your building control body whether the new structure needs an application, as a new roof frame generally does. A garage attached to the house has an additional dimension: how it joins the house wall, and whether the work affects a shared party wall or the neighbour's property.
Let neighbours know in advance. A scaffold, a crane lift and noise are all part of a conversion, and a friendly conversation beforehand is usually enough. If the garage backs onto a boundary, the overhang of the new eaves and gutters needs to be kept within your own land.
What it costs, and what you get for it
We do not publish a Beacon price for this, because every garage is different. As a guide to scale, a published cost guide gives a typical UK range of £1,200 to £2,500 for a fitted EPDM roof on a single garage, which is the sort of figure a pitched conversion will exceed several times over, since it includes a whole new frame, scaffold, covering, fascias, gutters and making good. In return, the roof is likely to last a great deal longer and may add storage space and kerb appeal. Our garage roof replacement cost guide covers the lower end of the scale. Your fixed quote follows the survey.
When to keep it flat
A flat roof is the right answer more often than people expect. If the garage is detached, tucked behind the house and out of sight, if the walls are weak, or if planning rules would limit a taller roof, a good flat roof does the job at a fraction of the cost. A warm-roof construction with proper falls and a quality membrane will not leak if it is built well. The leaky flat garage roofs people complain about are mostly old felt on a decayed deck, not a flaw in the idea of a flat roof.
The other reason to hold back is a plan to convert the garage into a room. If so, the roof needs to meet insulation standards and the structure might change again, so the two projects are better planned together. We cover that in our guide to the garage conversion roof.
Starting with a survey
If you are weighing a conversion, we start by looking at what you have: the walls, the span, the current roof, and any attachment to the house. We photograph the garage, tell you plainly whether the structure suits a pitched roof, and give you a fixed written price for the option you choose. If a simple re-cover is the sensible answer, we say that too. A ten-year written guarantee covers our workmanship. The work is part of our garage roof replacement in Basingstoke service, and the number to call is 01256 213956.
