The short answer
Most garages are better with gutters, because without them the roof dumps its water along one edge, splashing the walls and doors, soaking the ground and often running onto the neighbour's side. Nothing in the building itself forces you to fit them, so a small shed-style garage with a good gravel drip strip can manage without. Where the roof drains toward a boundary, a path or a door, fit them.
What happens to a roof with no gutters
A garage roof is a wide, smooth surface that collects rain and delivers it all to the lowest edge. In a heavy shower that edge sheds a curtain of water, which hits the ground hard enough to bounce back up the wall. Over a few winters the lower courses of brick or block turn green, the mortar softens, while the foot of the wall never fully dries.
On a timber-framed or timber-clad garage the effect is faster. Splashed water gets behind the cladding and into the sole plate, the timber laid at the foot of the frame, and rot follows. A metal or fibre cement garage suffers less, but its bottom edge can still rust or stain where the water runs.
The ground suffers too. A steady line of runoff cuts a trench along the eaves, washes soil from a flower bed, and in clay can soften the ground near the foundation. If the garage stands beside a drive or path, the same water can freeze there in winter and leave a patch of ice on a frosty morning.
When gutters are clearly worth fitting
Some positions make the case for you.
- The slope faces a boundary. Without a gutter, water drips onto the neighbouring ground. That is a common source of disputes, so catching and directing it on your own side avoids the argument.
- The slope faces a door or a path. Water falling across an entrance runs inside under the door and makes the approach slippery.
- The garage adjoins the house. Rain running down the party wall or the side of the house adds to damp that already exists.
- There is a long, low roof. A longer run carries more water to one edge, so the flow is heavier than on a short roof.
- You want a water butt. A garage roof is ideal for filling one, and a gutter and downpipe are the way to do it.
If two or more of these apply, the argument for guttering is strong.
When you can do without
There are garages where leaving the roof open is a reasonable choice. A small detached garage in the middle of a plot, with a roof that falls toward a bed or lawn, a wide gravel strip or a soakaway, causes little trouble. The same is true where the roof overhangs the wall by a good margin, which throws the water clear of the base.
A flat roof can also behave differently. Some flat roofs are built to fall to one edge with a small drip trim and no gutter, and the water leaves in a controlled way rather than running along the fascia. Whether that works comes down to the construction. The edge detail, and the ground beneath it, decide it.
The test is simple. Stand outside in heavy rain and watch the eaves. If the water falls clear and the ground soaks it up without splashing, a gutter may be a convenience, not a necessity. If it splashes the wall, runs along the ground or lands on someone else's side, fit one.
What a garage gutter run needs
A garage gutter is a short, simple run, but the details matter. The channel needs a slight tilt to the outlet so water drains instead of standing. A maker of small shed gutters suggests roughly 1:350 where the gutter is laid to a fall, and brackets no more than 500 millimetres apart, so the channel does not sag when it fills. Treat those as one maker's figures, and follow the instructions for the product you choose.
The outlet goes at one end, or in the middle for a long run, and feeds a downpipe, which carries water down to a drain, a soakaway or a butt. The downpipe should never discharge onto the neighbour's land or onto a path where it will freeze. A gutter is only as good as where the water goes next, so decide that first.
Gutter size matters less on a garage than a house, but a half-round channel with a decent depth copes with most roofs. A guard or leaf mesh helps where trees overhang, because a blocked garage gutter is rarely checked and fills quickly. A tree-lined plot can mean a clear-out several times a year.
Fixing it to the garage you have
How the gutter is fixed varies with the roof covering. On a pitched tiled garage the brackets go onto a timber fascia board, and that board must be sound. Rotten fascia holds nothing, so repair or replace it first. On a metal or fibre cement roof with no fascia, the gutter is usually held on brackets fixed to the rafter ends or to the purlins, the cross members the roof sheets rest on, using fittings made for that purpose.
Older garages may have grey asbestos cement gutters or a fascia that looks suspiciously like the same material. Leave them unbroken, and do not drill or saw into them. Our guides on whether your garage roof is asbestos and on asbestos surveys for garage roofs show how to find out, and what to do before any work starts.
A shed or workshop follows the same logic. Our page on outbuilding roofs covers sheds, workshops and studios, where gutters are one more edge detail to get right.
Deciding, and getting it done
So the decision is practical. Look at where the water falls, what it hits and who it reaches. If it lands harmlessly on your own soakaway, you can wait. If it splashes a wall, a door or the neighbour's boundary, fit a gutter, and do it when the roof is being repaired or re-covered, because the fascia and edge are bare at that stage and access is already in place.
When we survey a garage roof we look at the eaves and the ground beneath as part of the same job, and we say whether guttering would help and how it should drain. A written fixed price follows, and the rubbish is taken away when we finish. The wider garage roof replacement page explains how a full re-roof is approached, and you can ring us on 01225 285181 to arrange a visit.
