Posted By: Jeff B 20251. How can you ensure an airtight seal around the ring beam above the windows? The videos never show close ups of this.

Presumably lots of airtightness tape.

2. I can’t see how condensation can be avoided completely as outside air must surely be able to enter the space above the insulation via gaps in the ring beam.

More airtightness tape?

3. Should I really believe that the multifoil is as effective an insulant as 50mm of Celotex?

Dunno. We've done that topic to death over the years.

4. Won’t the space above the insulation become incredibly hot during the summer and affect the double glazing in the roof?

I'd guess so. They offer a tint to be applied to the inside of the glass, but I'd be tempted to whitewash/paint the outside of the glass too.

Our 'conservatory' is actually a sun room. It has a solid roof with a big opening rooflight. It also has lots of insulation in the walls and triple glazed windows. The spec was for it be above 30°C as often as possible (my wife comes from Malaysia). But it actually works pretty well and is usable all year.

I think I would go along with some of DJH's points above...

- paint the glass on the outside (eg https://www.rawlinspaints.com/products/772-coo-var-white-glass-shading.html}
- buy the multifoil (maybe get it cheaper from elsewhere?)
- fit it very carefully, with a good, expensive air tight tape. Remember it's not outside air you need to stop, it's air from inside the conservatory.
- Add timber battens with a second layer of VCL again taped very carefully, and fix a finish over that (the guys you linked suggest a thin PVC interior cladding (which you could source yourself).

If there's an occasional bit of condensation, you won't see it. Worst case there's more condensation than you hoped, and there's an occasional drip where it gathers at the base of the roof internally. It's likely a few hundred quids worth, and a bit of effort, and it will certainly be better in summer at the very least.

Posted By: Peter_in_HungaryWhat is your end goal ? making the conservatory all year around usable i.e. insulated to enable winter use or just to make it usable spring to autumn ?
If you want the latter then al you need to do is to mitigate the solar gain and the best way to do this is to put a screen of some type on the outside of the roof glass leaving the glass in place and any air tightness as existing.

If it is a square shape with glazing bars protruding above the glass then it should be possible to construct a false roof above the existing with light weight roofing panels leaving a small gap between the glass and the false roof to allow a bit of air flow. otherwise perhaps a retractable blind for use during the summer months might be an option. An inside blind would also work but would not be as effective. One advantage of a blind is that it can be retracted so the conservatory becomes usable on sunny winter days.

If the conservatory is not square then options become more complicated.

Thanks for your comments.

All year around. It's an Edwardian double hipped jobbie so with four triangular "faces". Probably the worst configuration to work with!

Posted By: GreenPaddyI think I would go along with some of DJH's points above...

- paint the glass on the outside (eghttps://www.rawlinspaints.com/products/772-coo-var-white-glass-shading.html" rel="nofollow" >https://www.rawlinspaints.com/products/772-coo-var-white-glass-shading.html}
- buy the multifoil (maybe get it cheaper from elsewhere?)
- fit it very carefully, with a good, expensive air tight tape. Remember it's not outside air you need to stop, it's air from inside the conservatory.
- Add timber battens with a second layer of VCL again taped very carefully, and fix a finish over that (the guys you linked suggest a thin PVC interior cladding (which you could source yourself).

If there's an occasional bit of condensation, you won't see it. Worst case there's more condensation than you hoped, and there's an occasional drip where it gathers at the base of the roof internally. It's likely a few hundred quids worth, and a bit of effort, and it will certainly be better in summer at the very least.

Thanks for your response.

The Rawlins paint is water-based and the glass is the self cleaning variety so I don't think the two would be compatible? I'm wondering if white uPVC 2mm panelling would do the same job, cut to shape and siliconed into place?

I think I'd be more concerned about the possibility of mould formation behind the insulation rather than the condensation per se. It might be better perhaps to not try to obscure the glass externally and allow the heat build up to remove the condensation and keep the moulds down?

So you recommend an additional VCL membrane on top of the multifoil as well. Do you mean on top of the second row of battens or over the first before the multifoil is attached?

Posted By: WillInAberdeenI had relatives with a lightweight poly carbonate roof who found the skinny roof structure supporting it couldn't carry any more weight, say for an insulated roof.

They were able to get a darkened grey polycarbonate sheeting fitted, which helped in summer. The multifoil product looks very lightweight, maybe aiming for this market.

Had it been glass (=heavy) the structure would apparently be strong enough for conventional insulation.

Eventually they had a local builder/joiner put up a new structural frame to support a slate roof with rafters, insulation, plasterboard etc. and now they use it year round. Obviously a lot more work and cost.

Thanks for your response. Yes, I've been thinking about using white uPVC sheeting externally. See my response to Green Paddy.

Can't afford one of the roof replacement systems sadly.

Could you put a warm roof buildup onto the outside of the structure - OSB-cellotex-EDPM? A flat-roof fitter might be able to do that fairly cheaply. Or tile-effect slate-effect sheets can be DIY.

Airtightness and decorative linings on the inside of the structure.

The glass could be removed, to free up weight, remove the condensation issue, and because it's no longer needed to see through.

Since the problem is solar gain rather than keeping heat in then an appropriate paint on the outside of the glass might be the easiest option
e.g.
https://technicalpaintservices.co.uk/catalogue/Solar-and-Heat-Reflective-Paints/
or
https://www.britanic.co.uk/product-page/solar-reflective-roof-and-glass-white-vinyl-paint-2-5l

Health warning - I have not used these products (and there are others) but you have a known problem with products on the market designed to solve the problem.

Posted By: GreenPaddyHi Jeff,

you mention the heat build-up removing the condensation. Where does it go? How does it get out?

The VCL layer I mentioned would go over the battens, as a further attempt to reduce vapour ingress towards the glass surface.

Something to cover the outside face of the glass I would suggest is a good idea, to reduce thermal gain, but mainly visually, as there will be "some" vapour under the glass, and it looks really bad, with steamed up glass panels. Not sure of the chemistry of the paint and self cleaning glass, and why it wouldn't work? Silicone around roof areas would not be a preferred option for me, as it will go black and gungey, and peel in time, trapping water between the PVC sheet and the glass - likely look a bit DIY. Paint is much easier to make look good quality.

Thanks for the ideas.

Re: where would condensation go. There are gaps to the atmosphere, admittedly small ones, where the DG units sit on the ring beam and also at the apex where there is a fat chunk of foam rubber located under the finial. Under this on the inside are a pair of "drip trays" which I presume are there to catch any ingress of water so I guess there must be the possibility of air ingress/egress there too?

Re: VCL. Sorry to be pedantic but which battens are you referring to? There would be two lots of battens. The construction from outside to inside would be:

Aluminium T bar (existing)
2 x 1 treated timber batten screwed into the above
Multifoil stapled to the above batten
2 x 1 treated timber battens screwed through multifoil into outer batten
White PVC T&G fixed to inner batten

Re: shading tint. I rang Rustins and they said that the CooVar shading tint is primarily for interior use. If used externally it would need re-application from time to time depending on the weather. N.B. it's pretty wet in west Wales! It would actually be easier to use on the inside from an accessibility point of view. I have noted previously when considering using reflective film on the inside that for some manufacturers of DG units this is a no-no due to increased stresses within the glass. Don't know if the same concerns would apply to the tint? Rustins (understandably) couldn't answer this question.

Yes, I agree with what you say about uPVC panels on the outside - inevitable that water would find its way under it and stain the glass although the silicone (or hybrid sealant) would be under the perimeter of the PVC panels rather than on the surface. Also if we went for internal roof insulation we wouldn't see it!

Posted By: Peter_in_HungarySince the problem is solar gain rather than keeping heat in then an appropriate paint on the outside of the glass might be the easiest option
e.g.
https://technicalpaintservices.co.uk/catalogue/Solar-and-Heat-Reflective-Paints/" rel="nofollow" >https://technicalpaintservices.co.uk/catalogue/Solar-and-Heat-Reflective-Paints/
or
https://www.britanic.co.uk/product-page/solar-reflective-roof-and-glass-white-vinyl-paint-2-5l" rel="nofollow" >https://www.britanic.co.uk/product-page/solar-reflective-roof-and-glass-white-vinyl-paint-2-5l

Health warning - I have not used these products (and there are others) but you have a known problem with products on the market designed to solve the problem.

Thanks Peter. See my comment above re the CooVar product.

I have had a look at the links you sent (thanks) and I see that the Technical Paints people do a solvent based product which I reckon might be ok on the self cleaning glass DG panels. I'll give them a call in the morning. Hopefully they can do me a small sample to try!

When I built my sunroom I separated it from the sitting room with full width, 4M wide, exterior grade bifolds. I didn't extend the house heating system into the sunroom, instead I fitted a freestanding WBS for Winter use. The sunroom roof is roughly 50/50 solid insulated and 2G glazed. One of the three walls N side is also solid insulated. I tried to strike a balance between light and airy, and Summer and Winter usage.

Re timber battens, fitting foil...

is there a need for the first layer of battens? Double sided tape the foil to the PVC frame (temporary hold), which presumably sits proud of the glass surface, giving the air gap glass/foil. Fix the timber battens over the foil into the frame. Add the VCL, with further careful taping. Add internal finish.

Posted By: djh

Posted By: Jeff B 2025unfortunately my lady CEO has vetoed any notion of me clambering about outside on the roof of our conservatory!

Maybe if you took the glass out as Will suggested (or had it taken out) the insulation work would be more accessible with no need to clamber on the roof?

Possibly! I think she make take some persuading.

Thanks all for the many thoughts and suggestions. Lots to think about before coming to a decision!