Copy this detail for a ‘warm roof’ design and its description onto your drawings for Building Control. Note that ‘cold decks’ are still allowed if you can design a continuous vent across the top of the insulation. A picture of this is shown on the Thermal page. We have also seen many situations where height has been a problem and the joist void has been completely filled with insulation or insulation is held tight below the decking ie there is no cold void to ventilate. In this case extra vapour barrier protection below the joists should be included.
Note on building a balcony as part of a new building:
The secret is to work DOWN from the final surface level when figuring out heights for the structural work. The Permadeck on its plywood deck is about 21mm thick, the insulation and vapour barrier will be ~100mm, the lower deck will be, ideally, 18mm and the firring (tapered pieces) will be ~50mm at the high end. That is a total of 189mm!! and that's BEFORE the threshold (step) is formed. The threshold should be a minimum of 75mm to the underside of the cill, which should have a lead apron below it as shown on the Balcony Prep page.
If the balcony is being cut into a pitched roof the lower edge of the balcony can be formed as a 'mansard', ie the upper deck should be projected over the tiles or slates below the balcony. Mansards
Permadeck is an excellent product for solving the problems of balconies but please talk to us before you build it! The commonest problem is thinking you can just project the floor joists out at the same level forgetting that a slope must be formed with a ply/insulation/ply sandwich on top and then there's the threshold and then the cill and then the door frame. By the time you've finish you'll need a ladder to get out! But done correctly a Permadeck balcony looks and works great.
Modern 'Mansard' - a flat roof on top of a slated or tiled pitch
Permadeck solves problems AND creates opportunities:
This rear extension is a conventional roof on one side and a mansard on the other.
Your designs can use the potential of Permadeck to the full: roofs can be ANY shape,
ANY colour, low or high traffic, cold or warm decks, roof gardens, lightweight roofs,
balconies, turrets, parapets, wet rooms etc.
If you are designing or building a new roof this is the gateway page to lots of technical
information. If you want to REFURBISH an existing roof CLICK HERE. Note that the
design suggestions here MUST be checked and confirmed by a competent person.
The navigation bar on the left shows all of the technical areas covered.
Permadeck’s BBA certification is for a waterproofing system. The certification does
NOT cover the roof design, which should be designed & approved by a competent person
prior to construction.
Don’t get lost! These are tech pages only, go to HOME for main page list
Permadeck 20 (BBA Cert 93/2967) in standard grey by Seamless Roofing Ltd with integral
heavy duty edge trims and flashings on pre-skinned Permadeck DryPly18™ 18mm plywood
on XXXmm Kingspan TR27 or equivalent on 1000g vapour barrier on 18mm sheathing ply
lower deck on tapered firring @ minimum 1:60 falls to external gutter with edges
kept horizontal all on XXX x XX joists and all secured according to the manufacturer’s
instructions and to suit exposure. Joist voids should be hermetically sealed and
regarded as part of the habitable envelope . Total U-value including plasterboard
ceiling better than 0.18”