Warm Flat Roof Joist Construction

Thermoplastic or elastomeric are the most effective and should extend up adjacent walls at least 150mm from the roof surface.

Warm flat roof joist construction.

Getting the balance right here is crucial as too much weight will inevitably lead to an unstable roofing structure. Flat roofing under construction plywood decking is then used to cover the joists with the width in between also determined by the weight being placed upon them. A thermal layer of fibreglass polystyrene or other insulating material should be inserted either above the roof decking the warm roof model which is suitable for homes or permanent residences. The major difference between the warm flat roof and the cold flat roof has to do with the air flow between the roofing timbers known as joists that help to hold up the roof.

Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. A warm deck roof is where the insulation is placed on top of the rafters joists and the roof covering is then placed over the insulation. A warm flat roof or a built up roof bur is one where all the insulation is above the joists deck making them part of the warm fabric of the building. The construction of the flat roof is similar to that of the timber upper floor.

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. Of course you don t need to live in a modern house to deal with a flat roof. The insulation is immediately below the waterproofing layer. No ventilation is required for these types of roofs.

Flat roofs aren t architecturally logical as rain and snow will shed much more quickly off a sloped roof. Constructing a warm roof on a new extension with parapet walls i will have surplus amounts of insulation left over and am considering adding this insulation to the underside between the joists to double up the insulation would this install have any negatives. The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. On a basic level flat roof construction comes in the form of roofing timbers or joists as they are more commonly known or steels that are laid across two uprights walls in most cases.

The vapour control layer is above the decking but below the insulation. Learn more about warm roof cold roof construction. In the warm flat roof construction there is insulation packed into every possible space where air can flow.