Well, as I've mentioned before, we are building a conservatory. It will be lean-to, with the frame built of timber and with a triple wall polycarbonate roof. We've built a conservatory once previously, and found that the roof space overheated, and cooked the uPVC brown in 5 years (and it was UV stabilised). We then put in a twin wall polycarbonate roof, with one kit roof vent - window that opened upwards - so hinged at the top, automatic opener at the bottom. Weren't too impressed with it as it wasn't that big, cost £70 and tended to leak in the rain. Where we are now is very exposed, whereas our last house was sheltered -we have to be extra careful on strength and sealing. So this time round we don't want to cut windows into the polycarbonate - what we are plotting is a crafty roof vent at the top of the roof - between the roof beams.
This is where the explanation gets a bit complicated. It is a lean-to conservatory, but is not leaning directly on the house wall (because the bungalow is too short). What we are doing, is basically mounting what would be the wall plate on pillars, and so the peak of the roof, will be a few inches higher than the house gutter. (We are also re-doing the house gutter to be a large gulley gutter that butts between conservatory "wall" plate and the house eaves.) This means that the beams which sit on top of the "wall" plate to support the polycarbonate, will have an air gap in between them. (So there will be a series of air gaps bounded by wall plate at the bottom, roof beams at either side, and polycarbonate at the top.) Obviously we need to fill this in to complete the conservatory insulation - but what we want to do is turn these into vents - but vents that are well sealed against water ingress when shut and form a good insulating barrier for winter. An ideal design would be something like those metal covers for the outdoor side of an airgap - series of vertical slots and you use a handle to slide a plate across to open or shut the gaps. We could use those, but it would provide no insulation at all. Is there a thick, insulating version of such a vent?

Have you got low-down vents at the opposite side? We have 3 roof-lights each side of a pitched glass roof and it just shifts hot air above our heads!!

Hi Shepherd,

sounds interesting, but why polycarbonate ? glass is about the same cost and would last you a lifetime. a company called Exitex in Ireland (i think that's the spelling) do all sorts of fixings for glass and PC. google it.

Tom

Hi HowdyTom
In an ideal world we'd prefer glass, but we were going for polycarbonate because of the weight. Each roof section would be 1m wide by 2.4 meters long (and approximately ten sections in the roof).

Using http://www.matweb.com/tools/weightcalculator.aspx I did a calculation based on purely two sheets of glass of that area, 4mm thick and that came to just under 42kg per section. (Then add the weight of the double glazed section frames.)

Looking at manufacturers data for triple wall polycarbonate, 16mm thick, the same area came to 6.5kg.

The slope of the roof, due to restrictions of the site, will be about 12 degrees (best we can manage, would like more).

We are also in an exposed area so will have quite a lot of wind loading on the roof. Possibly therefore want to have some form of special higher strength glass or greater thickness - don't know, didn't look any further into it. Like the polycarbonate box section support mechanism too.

CWatters
Snow, yes, forgotten snow, snowed today, hmmm. These theoretical vents did also have theoretically good sealing, but going off the idea. Starting to think about roof lights, maybe of the sort of caravan roof design, right at the apex of the roof. As in the hinges are under the apex cap of the roof, and the window slots down over a raised box frame. So much better roof lights than our last conservatory.