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Permadeck with  soft single ply systems

E&OE      The text and graphics of this website are Copyright © 1996-2015 all rights reserved by Seamless Roofing Ltd.  Permadeck, Thermadeck & Flexiroof are registered trade marks.  The contents of this website are subject to review and are a guide only and do not represent a binding offer. The BBA logo is Copyright © British Board of Agrément.  

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 If you’re building a warm roof, the above applies plus:
If fixing through insulation, Ebay can supply fixings long enough to screw through the upper ply down through the insulation and into the lower ply. The lower deck should be 18mm so that the fixings don’t protrude, eg 18+90+18 = 126 ie 120mm fixing countersunk and drawn down. It is sometimes better to get the fixings first and then vary the insulation to match.  Alternatively longer fixings can be used so long as they penetrate the firring/joists below.  Remember to fit your fascias and gutters because the Permadeck trims fix over them tightly.  This is a guide only, the joiner is responsible for correct and secure construction. Do NOT use foil-faced insulation. If using pre-felted insulation use felt side down as an additional vapour barrier.
If you’re fitting fascias and gutters:
Fascias should be held 2-3 mm below the final deck surface.
Tilting fillets, drip (doubling) rails and wall plates are not required.
Gutters should have their top edge running from 60mm to 75mm below the final deck surface.  This gives a 15 mm run over the whole length.  Extremely long gutters should have extra outlets. A horizontal gutter should be fitted 65mm below the final surface (use deep-flow).
If you’re building a balcony:
Read through the Architectural and BalconyPrep pages BEFORE you build ANYTHING or you may have problems with inside/outside heights, patio doors, ponding, abutment details, stanchion fixings etc.  
Note on ‘falls’ (slope):
From an appearance point of view a good slope is better than none or ponding.  For balconies we recommend a slightly GREATER fall than for just a flat roof.. However, nothing disastrous will happen if you have some ponding and at no time has Permadeck exhibited any adverse reaction to standing water.  This is in direct contrast to many well known liquid applied systems, but then that’s why fibreglass can be used for tanks, ponds, boat hulls etc. And why Permadeck is great for roof gardens and wet rooms.
This is representational of a cold deck, the firring will in practice run towards the gutter.
This is representational of a warm deck, the firring will run towards the gutter.
If using raw plywood it must be kept dry to ensure a 100% bond, see below for best type of plywood.
Seamless Roofing can supply Permadeck DryPly18™ pre-skinned 18mm ext wbp plywood.  This saves time and money trying to keep the timber dry.  We also offer a quick tape-up service to joint the pre-skinned boards giving an effective seal INSTANTLY (central Scotland only). Or the site joiner can butt joint the boards with a bead of frame sealant, though NOT silicone or use a temporary 50mm duct tape over the joints.
If you’re building a cold deck, like a garage roof:
Boards should be securely and evenly laid and be staggered in at least one direction on roofs over 50m2. Falls should be between 1:80 and 1:40, ie a 4m run should use 50mm to 100mm firring sloping to 0mm.  Expansion gaps of 10 - 20mm should be left at wall abutments so if the boards swell they don’t buckle up.  The boards themselves should be butt jointed.  Each 8 x 4 sheet should be secured by a minimum of 4 rows of 5 fixings, Paslode sheradised ring nails are ideal.
Information for joiners preparing decks for Permadeck

60 -75mm

60 -75mm

This is representational of a warm deck with an internal gutter.  The gutter should also have a fall to the outlet of at least 1:80. Both layers of decking require a minimum of 4 rows of 5 fixings per 8x4. Fixings should be countersunk and secure.

This ‘double’ extension was well made - the far end will be a balcony.  This picture shows the Permadeck just before the final colour coat.  The site joiner used 18mm Permadeck DryPly™ to box in the deck & parapets and form a kerb for the cupola.  The falls & cross-falls were carefully designed to lead the water through the parapets to the two hopper outlets at either end.

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Note on Plywood
Permadeck should be laid on dry Ext WBP softwood ply, which is rated Structural and have one good face laid uppermost.  Avoid Marine and Far Eastern plywood as less of the resin soaks into the grain affecting the potential bond.

Film Faced plywood, often sold as exterior ply, should not be used because the paper-thin veneer is inadequate as a bonding surface.