The Lay­ered Roof

TV pre­sen­ter and ar­chi­tec­tural de­signer Char­lie Lux­ton ex­plains why count­less lay­ers (and de­tail) have gone into cre­at­ing his su­per-in­su­lated, flat green roof

Homebuilding & Renovating - - On Site -

One of the big­gest el­e­ments of any self-build is the roof. Get­ting it right is ab­so­lutely cru­cial. When you have a rel­a­tively sim­ple piece of ar­chi­tec­ture like this house – a rear wall that sits into the hill­side, a front façade and a roof is the sum of the ar­chi­tec­tural ex­pres­sion here – the roof is a mas­sive part of the over­all build and the de­sign.

We used a pre-cast con­crete sys­tem; on top of that there are mul­ti­ple (seem­ingly end­less) lay­ers of ma­te­rial that go on in or­der to cre­ate our durable and well-in­su­lated roof.

We started off with the con­crete plank, and then used a primer on top. On top of the primer we in­stalled a very thick torch-on vapour mem­brane, which is also a wa­ter­proof layer, to pre­vent mois­ture from the build­ing ris­ing into the in­su­la­tion and con­den­sat­ing. A big part of the prob­lems as­so­ci­ated with early flat roofs, in the 1950s and 1960s, was con­den­sa­tion — so this is our so­lu­tion.

Then we’ve laid on a Kingspan ta­pered in­su­la­tion sys­tem. While the roof is flat, all the in­su­la­tion is cut to fall, so the wa­ter runs back to­wards the out­lets. That’s all done within the in­su­la­tion layer, so you have to get some­body to sur­vey the roof and then get the pan­els as­sem­bled for your roof — it’s quite a be­spoke el­e­ment.

On top of the in­su­la­tion goes an­other layer of wa­ter­proof­ing, and on top of that is the most im­por­tant el­e­ment of what will be our green roof: the root-re­sis­tant layer. We’ve used Ico­pal Root­bar, which has a green hue be­cause it has cop­per in it. That will stop the roots of the grass roof grow­ing through the mem­brane, which, as you could imag­ine, would be cat­a­strophic on a flat roof.

And there’s an­other four or five lay­ers on top of this that are as­so­ci­ated with the green as­pect of the roof: fleeces, drain­ing lay­ers, gravel lay­ers, soil and then the grow­ing layer. Green roofs, while lovely and cru­cial to this piece of ar­chi­tec­ture, are time-con­sum­ing and com­pli­cated.

The roof ranges from about 150mm of in­su­la­tion on one side to about 240250mm on the other — so it’s quite a fall. It means the roof has an av­er­age U value of 0.12W/M2K, which shows it’s a high-per­form­ing roof. It’s made a huge dif­fer­ence in­side — you can feel the tem­per­a­ture change in the build­ing and there’s been a re­duc­tion in con­den­sa­tion in­side, too.

With the roof laid, we are fully weath­er­tight — which means we’re ready to start in­side.

Next month: The heat­ing and ven­ti­la­tion sys­tems

Com­plex Roof Struc­ture

Char­lie has de­vised a mul­ti­layer sys­tem that sits on top of a pre-cast con­crete ‘plank’ for his green roof, in­clud­ing wa­ter­proof­ing, in­su­la­tion and a root-re­sis­tant layer.

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