Flat roof answer
Does a flat roof take a sun tunnel?
It can, and a flat roof is often where a tunnel does its best work. The detail lies in the base, the thin build-up and the short drop beneath, all of which we look at before a price is given.
The answer
Yes. Flat-roof sun tunnels sit on a raised base, called an upstand or kerb, that the waterproof covering is turned up against. The dome stands a little proud of the roof, so its height counts against the permitted development limit on a house. On a flat or maisonette, the council must grant planning permission. The drop beneath is short, which suits the light.
How is a tunnel fixed to a flat roof?
On a kerb or upstand fixed around the opening. The roof covering turns up its sides and the dome sits on top, so water is kept out and the dome is lifted clear of standing water and snow.
A pitched roof sheds water on its own. A flat roof does not, so anything that pierces it has to stand up out of the water line. That is the job of the upstand.
What the base does
The base is a short collar of timber or a moulded kerb, fixed round the hole. The roofer turns the waterproof layer up its outside face, and the dome base then clamps over the top. Manufacturers set minimum upstand heights, commonly around 150mm above the finished roof, to keep rain and snow away from the joint. That figure is a common manufacturer setting, not a rule for every product.
Flat-roof kits
Sun tunnel makers sell kits made for flat roofs, where the dome sits on a flat base instead of a flashing designed for tiles or slates. The kit is chosen to suit what is on your roof now, be it felt, single-ply or a liquid-applied coating, with the upstand built as the maker directs. Our page on upstands and kerbs explains the detail.
Does the raised base cause a planning problem?
It can. On a house, the dome and its base count towards the 150mm limit above the roof, so a tall upstand may use up the allowance. A flat is different: the council must grant permission whatever the dome's height.
The raised base that keeps the water out is also what makes a flat-roof tunnel more noticeable than one on a slope, and it is the part the planning rules look at.
On a house
A rooflight on a house is permitted development under Class C if it projects no more than 150mm beyond the plane of the roof slope and sits no higher than the highest part of the roof. Here the measurement runs from the roof surface up to the crown of the dome. If the upstand and the dome together rise higher than 150mm, the tunnel falls outside Class C and a planning application is needed. A low-profile dome on a low base has the best chance of staying within it. An Article 4 direction, or a condition on an earlier permission, can remove Class C from a house. A conservation area alone does not take Class C away.
On a flat
Flats and maisonettes have no householder permitted development. A Tyneside flat with a flat-roofed back offshoot therefore needs planning permission from the council for a new tunnel, upstairs or down. Our planning answer looks at houses and flats separately.
What is under a flat roof, and does it suit a tunnel?
A flat roof has a shallow build-up of deck, insulation and ceiling, so the drop is short and the light strong. The tube must pass through the insulation without letting cold or damp across it.
The depth between a flat roof's top and the ceiling of the room is small, often not much more than the joists. That short distance is good news for the light, since little is lost on the way down.
Joists and trimming
The tunnel has to fit between joists. If the opening lands on a joist, we move it along the roof to clear one, or frame round the gap with trimmers, which is building work notified to Building Control. We send the Building Control notification where one is due, and the framing round the opening is among the things looked at.
Insulation and condensation
A flat roof is one assembly, and cutting through it breaks the insulation unless the work is done with care. The tube is sleeved and sealed through the build-up, and the diffuser has a thermal break, so warm air from the room cannot reach cold surfaces. The roof side of the job is explained on our flat roof rooflights page.
Our view: a flat roof suits a tunnel well, as long as the base height, the joists and the waterproofing are planned together.
Which flat-roofed rooms get the most from a tunnel?
Back offshoots over a kitchen or bathroom, single-storey extensions, utility rooms and porches. Each has a short drop, and a small tunnel brings daylight without a large opening in the roof.
Flat roofs turn up in a handful of places on Tyneside homes, and each calls for slightly different thinking.
Back offshoots
A rear offshoot may have a low flat roof over the kitchen or bathroom. A tunnel lights an inner bathroom or a dark corner of the kitchen without the cost and size of a large rooflight. For a downstairs flat, the offshoot may be the one place a tunnel is possible. Ownership of that roof is set out in your title or lease, so read it and consult the other owner prior to ordering.
Extensions
A single-storey extension suits a tunnel over a utility, a pantry or a corridor, leaving the main room to take a lantern or a flat rooflight. Compare them in our sun tunnel or rooflight guide.
Porches and garages
A garage converted to a room, or a porch, can take one for a modest amount of daylight where windows are small. The route is short and the roof is usually simple. We look at each on the free survey.
Flat roof tunnel questions
Will a flat roof tunnel leak?
Not if the upstand and the waterproof covering are built properly together. The covering turns up the base and the dome is sealed onto it, as the maker specifies. The base height keeps water and snow clear of the joint.
Can the tunnel go through a roof with a green or gravel finish?
Yes, but the finish has to be cleared back around the base and the covering detailed to match. We confirm what the roof is made of at the survey, because the kit and the upstand depend on the covering.
Is a flat roof tunnel noisy in the rain?
A dome can carry a gentle patter, and the tube and ceiling panel soften it. Fitted tightly and sealed, it is not usually disturbing. A bedroom may want a quieter dome choice, which we can talk through at the survey.
Do I need a loft above for a flat roof tunnel?
No. With no loft at all, the tube is as long as the roof build-up is deep. That is one reason a tunnel fits so neatly into extensions and offshoots.