flat roof install from scratch

[mpheating]

hi, my builder has almost finished building the shell of my garden office which is 3 metres wide x 5 metres long (slope is going to be 3m direction)

I am going to install the roof and joists myself to save on money, I am a tradesman but not in this line of work so I just wanted to make sure I was going along the right lines, all help would be much appreciated.

I am thinking the following materials:

150mm x 50mm x 3000mm joists @ every 600mm centres x 10
sub deck 11mm sterling board
100mm celotex insulation board
top deck 18mm sterling board
epdm rubber membrane


I am unsure on how to fix my joists and also fix the insulation to my sub deck and my top deck, can you buy really long screws?

I was thinking of securing some kind of 4 x 2" wall plate on my internal brickwork as I have a 100mm cavity, and using wall plates to secure the wall plates to my internal breeze blocks. Then screwing my joists down to the wall plate, spamming the joists down the centre to make it nice and secure. Then installing firrings "2 to 0" for a slope.

Joists cut level with end of external brickwork and upvc cladding installed before rubber membrane??

I have looked everywhere for pictures of how to install the joists and rubber membranes but not found any good ones.

Also if anybody could suggest the best place to buy epdm firestone kits from it would be much appreciated.

Thank you.

 

[ban-all-sheds]

You forgot the vapour control layer.

http://images.google.com/images?q=flat+roof+detail

 

[mpheating]

what is the vapour control layer, it is like a membrane sheeting that you can buy from the merchants, and how do you secure it, screw the above insulation/boards through it?

thank you

 

[ban-all-sheds]

A vapour layer should be positioned under the insulation or, in some situations, immediately below the roof covering to minimise water vapour condensing beneath the membrane.

Vapour control layer may be formed using any of the following:

• A polythene sheet membrane loose laid and restrained by mechanical fasteners or nailed to the deck (timber decks) all laps should be sealed with an appropriate adhesive.
• A reinforced bitumen sheet. - one layer of BS 747 Type 5U felt, fully bonded or mechanically nailed to the deck.
• Two layers of Type 5U felt fully bonded in hot bitumen. check - all laps must be sealed with bitumen.
• For single-ply membranes, the VCL should be either polythene or reinforced aluminium foil.

You can also get insulation with a foil VCL bonded to one side, but you need to run a bead of mastic along the deck where the joins are - I'm sure that the Celotex/Kingspan/Knauf websites will have details of suitable products.

 

[catlad]

I would reduce the 600mm centres to 400mm.

 

[mpheating]

ok I can do 400mm that's not a problem, id rather it be strong.

there is two things bothering me..

1. will my builder finish the 2 courses of brickwork, internal external at the same height, and then I fit the wall plate on top of the internal blocks to extend the height, or should the internal height be the same as the outside on completion of installing the wall plate?

2. the insulation I am going to use for the roof is celotex, it does have a foil on either side, is this a vapour barrier? if not could I use damp proof membrane as I bought a huge 25metre roll for foundations