Insulating conservatory roof. How to attach batons?

bflare

Hello. I have a simple lean-to-conservatory built-in 2000 & relatively small at 2m x 3m. My plan was to attach some 2x1 batons horizontally & in between these lay some YBS superquilt multi-layer reflective foil insulation. Then attach some vertical batons to the horizontal ones which will give the recommended 25mm gap. Then clad with PVC cladding. However, I am not sure how to attach the batons to the roof? Is it just a case of using something like Gripfill? I would have rather screwed them to something but that would mean drilling through the polycarbonate roof sheets into the what look to be relatively thin metal runners which I have circled in red in one of the pics. Is this a viable option?

FreeBear

Personally, I wouldn't use a multifoil quilt regardless of how brilliant the manufacturers claim it is. If you want a worthwhile lightweight insulator, you can't do much better than Celotex/Kingspan type boards. Whilst the Superquilt may be good at reflecting radiant heat, it has a low resistance to conducted heat - If you look at the YBS datasheets, in most applications, they recommend a secondary layer of Celotex/Kingspan.

Bendy_House

I agree with FB. A rigid insulation board will be far more effective, and also easier to use.

Even the thinnest ~1" will do a lot, tho' try and go for 2" or whatever  you can.

Could you provide a close-up photo of these rails? How wide is the visible contact part on the underside? And do they stick down below poly roof level, or are they flush?

I think my approach would be:

1) Mark on the bottom wall plate and on the house wall the centres of each rail!

2) remove any foam or rubber seal from along the lower roof edge that's sealing the polycarb to the top of the window wallplate - you ideally want trickle ventilating going on between the underside of the polycarb and the new insulated ceiling. This should not compromise waterproofing, as the roof panel overlaps that point - yes?

3) use StixAll or similar to adhere your 2x1s to each Ali joist. If the timber battens are slightly bowed, then place their convex middles upwards against the joists, and prop each end up with spare battens from the ground until they stick. Add a bit more StixAll to the 'trying-to-pull-away' end parts. Leave for a day. They'll now be stuck.

4) cut the Celotex-type insulation to fit as neatly as you can. Ideally mitred at each top & bottom end where they meet the window and house walls at a small angle. If you don't, then the window end can easily be filled with a bead of foam, but the house end will have a tiny void in the join. In any event, I'd run a small bead of foam along the edges before fixing them in place, and that includes between sheets.

5) Fix the sheets in place using StixAll - it'll be more than strong enough. As before, prop up to flatten any bows until it sets. Since your (more unusual?) roof has lots of joists, I wouldn't worry about cutting the sheets so joins land in the middle of a batten, I'd just foam the ends together wherever, tho' make sure they are flush with each other, which they should be.

6) trim away any extruded foam once set. I guess you can also foil-tape each join, and also the perimeter, tho' with the latter, just bring the return on the wall down no more that the cladding will cover - around 10mm?

7) fit the cladding. Your choice - panel pins through to the battens. Screws. StixAll.

8) Happy New Roof

9) PLEASE post stage-by-stage photos of whatever you end up doing, along with updates on how it performs. Insulating conservatory roofs is a constant theme on here, and I think it'll be of significant interest.

How many years have you already lived there? How well do you know how it currently performs?

Good luck

Bendy_House

bflare said:

I haven't seen a poly roof like that before.

Anyhoo, that's this year's project.

Next year's is:

https://www.the-roofing-contractors.co.uk/plastic-roof-tiles/ :-)

(I am not recommending that specific make - it's just an example.)

FreeBear

Bendy_House said:  4) cut the Celotex-type insulation to fit as neatly as you can. Ideally mitred at each top & bottom end where they meet the window and house walls at a small angle. If you don't, then the window end can easily be filled with a bead of foam, but the house end will have a tiny void in the join. In any event, I'd run a small bead of foam along the edges before fixing them in place, and that includes between sheets.

On the subject of expanding foam - Use a foam gun. It is much easier to lay down a thin bead than with a can with a built in nozzle. Working overhead, you need to attach a short length of flexible tube to the end of the gun. With one hand, squeeze the trigger on the gun (keeping the canister vertical), and with the other hand, guide the end of the tube to where you need the foam.

Cutting Celotex type boards - Don't use a hand saw. It makes a lot of mess. Instead, raid the kitchen for a sharp serrated knife. I use a 4" Kitchen Devil (code: 602003), but a really sharp bread knife would also work..

bflare

Bendy_House said:

I agree with FB. A rigid insulation board will be far more effective, and also easier to use.

Even the thinnest ~1" will do a lot, tho' try and go for 2" or whatever  you can.

Could you provide a close-up photo of these rails? How wide is the visible contact part on the underside? And do they stick down below poly roof level, or are they flush?

I think my approach would be:

1) Mark on the bottom wall plate and on the house wall the centres of each rail!

2) remove any foam or rubber seal from along the lower roof edge that's sealing the polycarb to the top of the window wallplate - you ideally want trickle ventilating going on between the underside of the polycarb and the new insulated ceiling. This should not compromise waterproofing, as the roof panel overlaps that point - yes?

3) use StixAll or similar to adhere your 2x1s to each Ali joist. If the timber battens are slightly bowed, then place their convex middles upwards against the joists, and prop each end up with spare battens from the ground until they stick. Add a bit more StixAll to the 'trying-to-pull-away' end parts. Leave for a day. They'll now be stuck.

4) cut the Celotex-type insulation to fit as neatly as you can. Ideally mitred at each top & bottom end where they meet the window and house walls at a small angle. If you don't, then the window end can easily be filled with a bead of foam, but the house end will have a tiny void in the join. In any event, I'd run a small bead of foam along the edges before fixing them in place, and that includes between sheets.

5) Fix the sheets in place using StixAll - it'll be more than strong enough. As before, prop up to flatten any bows until it sets. Since your (more unusual?) roof has lots of joists, I wouldn't worry about cutting the sheets so joins land in the middle of a batten, I'd just foam the ends together wherever, tho' make sure they are flush with each other, which they should be.

6) trim away any extruded foam once set. I guess you can also foil-tape each join, and also the perimeter, tho' with the latter, just bring the return on the wall down no more that the cladding will cover - around 10mm?

7) fit the cladding. Your choice - panel pins through to the battens. Screws. StixAll.

8) Happy New Roof

9) PLEASE post stage-by-stage photos of whatever you end up doing, along with updates on how it performs. Insulating conservatory roofs is a constant theme on here, and I think it'll be of significant interest.

How many years have you already lived there? How well do you know how it currently performs?

Good luck

Thanks for your reply and instructions. The problem I'm having is that the ali rails are not visible if you get what I mean? They are within the roof. So not sure what to attach the buttons to? 

These are some more pics. 

Bendy_House

PROVIDED the polycarb underside layer is securely attached/part of the Ali joists, then I'd have no concerns in adhering the battens straight on to the poly surface on the ceiling, immediately under where the joists are positioned. Give the to-be-glued stripsof polycarb a good scouring first, tho', to ensure they are clean and ready for the adhesive.

StixAll is superb stuff - very sticky, very tough, gap-filling, and rubbery in consistency when set. Once stuck, it ain't coming off...

I don't see any issues at all.

bflare

Bendy_House said:

PROVIDED the polycarb underside layer is securely attached/part of the Ali joists, then I'd have no concerns in adhering the battens straight on to the poly surface on the ceiling, immediately under where the joists are positioned. Give the to-be-glued stripsof polycarb a good scouring first, tho', to ensure they are clean and ready for the adhesive.

StixAll is superb stuff - very sticky, very tough, gap-filling, and rubbery in consistency when set. Once stuck, it ain't coming off...

I don't see any issues at all.

Brilliant thanks! Another question. When I place the Celotex-type insulation between the batons do I seal any potential gaps between the insulation & batons with foil tape or expanding foam? 

I have ordered some StixAll so think I may start on this project shortly. 

I have found these pics on the net which looks like a similar roof to mine & I am assuming this is the type of design you mean although they have used aluminum batons & what looks to be polystyrene insulation. Would you run the batons in the same direction as shown here?

FreeBear

bflare said: Another question. When I place the Celotex-type insulation between the batons do I seal any potential gaps between the insulation & batons with foil tape or expanding foam?

Expanding foam to fill the gaps (see my note earlier about attaching flexible tube to gun). Cover the joints with aluminium tape from somewhere like Toolstation. Don't use the stuff that Screwfix sells as it is thin metalised plastic. Some would argue that taping the joints isn't necessary, but doing so will limit moist air from below getting into the insulation boards.

Bendy_House

That Ali structure appears fully self-supporting, and the installer clearly thought they shouldn't rely on the existing roof to take the 'weight'. I guess they could have run these joists in either direction, but chose widthways.

And, yes, it does look like 'Jablite' expanded polystyrene insulation, which is 'ok', but not nearly as effective as Celotex.

You are in the fortunate position of having LOTS of Ali joists to adhere to, so your ceiling should be sturdy. When you think of it, your poly roof is designed to take the weight of a shedload of snow without deflecting or coming down, so it should handle a couple of sheets of Celo and some lightweight cladding - very evenly dispersed - with no issues.

And... Is that condensation that's visible on that Ali? Even if it isn't, every single one of these joists is a thermal bridge! What a weird design...

I'd stick to your own plan

Bendy_House

Yes, run a tiny bead of foam along each board edge as you fit them, and ditto around the perimeter. You want your ceiling to be an unbroken layer of quality insulation. Add Ali foi tapel if you wish - it ain't expensive.