The short answer
Usually it is a good idea. A garage roof without guttering drops every drop of rain along the wall below it, which splashes brickwork, soaks the door frame and can undermine the ground beside the foundations. Guttering collects the water, carries it along a gentle fall to a downpipe and delivers it to a drain, soakaway or water butt.
Some garages have never had gutters and seem fine. Others have gutters that overflow every storm. Both are worth a look.
What happens without a gutter
Rain falling on a garage roof has to go somewhere. With no gutter, it runs to the lower edge and falls in a curtain. The ground below turns to mud or erodes into a trench. Splashback stains the lower courses of the wall, and brickwork that stays wet is open to frost damage, moss and algae.
Does a garage door suffer too?
Yes, if the roof edge sits above it. Water landing on the threshold runs under the door, soaks the bottom rail of a timber door and corrodes a metal one. An up-and-over door with a damp track will stiffen and rust. Water that lands beside the foundation can also soak into the ground and, in time, affect the soil under the slab.
On a house-attached garage the problem is worse. Water running off the garage can splash the house wall and soak damp-proof detailing. Some garages shed onto a neighbour's side, which is a dispute waiting to happen. A gutter keeps your rain on your side.
Not every garage needs one. A roof that drains away from walkways onto a gravel strip or planted bed may cope. The survey looks at where water goes and what it does when it arrives.
Getting the slope right along a garage gutter
A gutter is not level. It slopes gently toward the outlet, the point where water drops into the downpipe. Brett Martin advises 1mm of fall for every 600mm of gutter, which is a very small slope, easy to lose if the brackets are spaced too far apart or the fascia bows.
Why does my gutter hold water?
Water that stays put after rain tells you the slope has been lost. Sagging brackets, a warped fascia or an outlet blocked with leaves are the common culprits. A gutter that holds water gets heavy, pulls its brackets loose and grows weeds. Fixing it means re-hanging the run to a proper fall and clearing the outlet.
Size matters as well. A small roof can drain into a narrow gutter, and a longer run may need an outlet at each end or in the middle. The downpipe should be fixed firmly, with joints that overlap the right way. BS EN 12056-3 covers the layout and calculation of roof drainage, and sensible gutter and outlet sizes follow from the roof area and the rain it has to shed. The survey confirms what your garage needs.
Flat roofs add one more point, covered on our garage roof drip edge page: the roof edge must throw water into the gutter, not behind it.
Where the water goes
Collecting water is only half the job. It also has to leave. A downpipe can connect to a surface water drain, run to a soakaway, a pit filled with stone that lets water seep into the ground, or empty into a water butt.
Can I connect to the house drain?
That depends on what is already buried in your plot, so it is a question for building control before any pipe is joined. Somerset Building Control is on 0300 303 7790 if you are unsure. Where the position of a drain is unknown, a drainage specialist traces it first, and the downpipe waits for the answer.
A water butt is simple and useful for a garden. It needs an overflow that connects to the drain or soakaway, so a heavy storm does not flood the base. The butt sits on a firm, level stand, since a full one is heavy.
On the Somerset Levels, where the ground can already be saturated, where rainwater ends up matters more. GOV.UK has a tool to check your address, which is worth a look before you plan a soakaway.
New gutters, repairs and cost
Plastic guttering is common on garages because it is light, quick to fit and needs no painting. Cast iron and aluminium are other choices. The material matters less than the fall, the brackets and the outlets. A good installation lasts a long time, and a rushed one sags within a season.
Can the old gutters stay?
If they are straight, clean inside and joined firmly, a clear-out and re-seal may be enough. If the brackets have rusted, the joints leak or the run is cracked, replacement is the better buy. The fascia that carries them gets checked as well, because a rotten board will not hold new brackets.
A garage run is a small job beside a whole-house gutter replacement, and the survey sets the price for yours. Bracket spacing, the length of the run, access and the condition of the fascia all play a part.
See our leaking garage roof page for how we separate gutter faults from roof faults, and the garage and asbestos roofs page for the wider service. Photos of the gutter and fascia come with the written total.
More on garage drainage
Can a garage gutter drain onto the neighbour's land?
It should not. Water from your roof is your responsibility, and sending it over a boundary risks a dispute with the neighbour. The gutter and downpipe should deliver the water to a drain, soakaway or butt on your own ground.
How often should garage gutters be cleaned?
At least once a year, and again after autumn leaf fall if trees overhang the garage. A gutter that fills with debris overflows and soaks the wall below it. We can clear it and check the slope of the run at the same visit.
The full picture: Garage and asbestos roof replacement in Taunton ยท More short answers