Very simple trusses work on a principle of thirds.
Timber frame flat roof detail.
The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls.
This article describes and illustrates the different types of support that prevents roof sagging and wall bulging at buildings including definitions of collar ties rafter ties and structural ridge beams.
A super basic a frame roof will require anywhere between 4 and 8 depending on the size of the rafters with plumb cuts necessary for each angle in the brace.
The abutment detail of a flat roof is vital in order to prevent moisture penetration.
Timber in the form of rough sawn or planedboards or planks can be used as the loadbearing deck to a flat roof fig.
3 06 timber frame timber flat roof 3 07 timber frame timber flat roof with parapet 3 08 timber frame lintel at window head 3 09 timber frame windows and doors jambs and cills specification within an example should 3 10 timber frame ground bearing floor insulation above slab 3 11 timber frame ground bearing floor.
Dormer in section 3 11.
The insulation is below the deck but above the plasterboard.
For additional stability you can also use steel joists that are built into one or both of the walls.
The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure.
Parapet detail joists perpendicular 3 13.
Boardsmust have a nominal thickness of min.
Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls.
Refurbishing an existing timber joisted flat roof which has no insulation.
A cold flat roof is one where the insulation is between or between and below the roof joists.
Dormer in perspective view 3 12.
Parapet detail joists parallel details in section 4.
Some of these can support the roof and prevent ridge sagging and wall spreading.
Flat roof joist and decking 3 10.
This is used for refurbishment e g.
Similar to the abutment of a lean to roof lead flashing is chased into the external block allowing it to overlap the lead upstand coming from the tiles.
Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading.
Roof panels 3 8 1 roof panel connections 3 9.
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.
Collar ties rafter ties tension beams structural ridge beams.
24 mm 20 and should have.
