Constructing a Warm roof

[jassdhali]

Guys,

Using 12mm WBP as deck 100mm Celotex then another 6mm WBP before laying on the EPDM Layer.
Question is what fastener do I use to secure Celotex to deck & what fastener to use to fasten top WBP layer to the whole lot.
Thanks

 

[Blagard]

Your base deck seems undersized to me,

But to answer your question, you would normally fasten the top sheet through the insulation to the bottom deck (long galvanised screws). However even your top deck is a bit on the thin side to accept mechanical fixings, so you should consider PU Glue for the insulation to base deck and the top sheet to insulation.

Check the size of your base ply deck before proceeding.

 

[^woody^]

I think you can get away with the 12mm bottom board, but use 12mm as the top board too.

Glue the celotex to the bottom board, and then if you glue the top board to the celotex too, you will have a strong composite deck which compensates for the slightly undersized boards

The only problem with gluing the top board is that if at some future time the roof leaks/or cover needs replacing, then if the board needs to be replaced too, then it can be difficult to remove on its own

You need to get some special long screws with a wide flat head - not just normal countersunk ones

Make sure you bond all the boards and insulation so that no joints are in line

 

[jassdhali]

Cheers guys,

I can change the depth of WBP thats not really an issue - but trying to find a company online that does the fasteners is
I would however prefer to mechanically fasten rather than glue down.

 

[Alastairreid]

http://www.twistfix.co.uk/products/insulation-fixings-products.html?gclid=CK7e_N_D26oCFUkf4QodqlPv7Q

 

[^woody^]

Screwfix sell them - look for Heco Topix flange screws, or look at www.rcsfixings.com and their flat roofing screws

 

[JohnD]

what sort of glue should be used to create the rigid composite deck?

Edit: PU glue?
what like
http://www.ebay.co.uk/itm/500ml-PU-...ies_Carpentry_Woodwork_ET&hash=item2eb42c825b
?

Never come across it. Will it stay tacky while you spread or brush it across an 8x4 sheet of ply, ir does it set too fast?

How you you spread it?

 

[jassdhali]

Cheers guys,
Would be totally lost without you. I have seen the twistfix ones - but dont want to use nails in the event I do cock up & need to pull the roof apart, so the screws are definetely the option I will go for.

 

[JohnD]

Is there a slow-setting PU glue for large areas?

 

[theoldun]

Jass

If your joists are at 400 centres, roof only has occasional traffic and you are using CelotexTD4000 or Kingspan Thermaroof TR3, then you do not need a bottom deck, as sheets run parallel to joists with noggins across short ends.
6mm ply is standard for top deck.
Use ISF 18 fasteners straight through ply, insulation and into joists. Sizes 145mm 170mm 195mm. Penetration into joists approx 35mm. Buy ISF adaptor and drive in with hammer or SDS drill. If only few sheets to fix, you can drive them in with a hammer. Obtainable from the link above by alastairreid. Allow 16 fixings per board.
Warm decks should always be mechanically fixed.
oldun

 

[Blagard]

Jass

If your joists are at 400 centres, roof only has occasional traffic and you are using CelotexTD4000 or Kingspan Thermaroof TR3, then you do not need a bottom deck, as sheets run parallel to joists with noggins across short ends.
6mm ply is standard for top deck.
Use ISF 18 fasteners straight through ply, insulation and into joists. Sizes 145mm 170mm 195mm. Penetration into joists approx 35mm. Buy ISF adaptor and drive in with hammer or SDS drill. If only few sheets to fix, you can drive them in with a hammer. Obtainable from the link above by alastairreid. Allow 16 fixings per board.
Warm decks should always be mechanically fixed.
oldun

The OP is using EPDM. If Celotex TD4000 is used a further 12mm ply is needed on top.

 

[^woody^]

Is there a slow-setting PU glue for large areas?

I am almost sure that the same water-based contact adhesive that the OP will use for his EPDM, will do to stick the insulation to the ply

Brushes on easy with a paint roller and you get about 15 minutes

 

[jassdhali]

I was going for Celotex GA4000. Should I still employ a sandwich of 12mm WBP for it?

 

[^woody^]

IMO, non-glued 6mm ply as the deck is too thin - flexes too much, pulls down around the fixings too much, and more chance of edges bowing upwards

You can use it, but that's what I think

 

[jassdhali]

12mm sandwich it is then.. yummy