Roof framing in Batumi and Adjara: rafters to the design

Roof framing: what holds the roof up

Roof framing is the timber or steel structure that carries the covering, snow and wind and transfers them to the walls. It decides whether the roof is still straight in ten years and how it behaves in an earthquake. Rafter sizes, spacing and connections are calculated by the engineer from the span, pitch, covering weight and the snow load of the area, and on site we build the frame exactly to the drawing.

Purlin-supported and tied rafters

Purlin-supported rafters rest at the bottom on the wall plate and at the top on a ridge purlin carried by posts on an internal load-bearing wall. This is the most common arrangement in private houses: it is simple and carries a heavy covering. Tied rafters do not rest on the middle of the house; their lower ends are joined by a tie, and the whole frame works as a triangular truss. They are used when a large room without supports is needed under the roof, such as an attic hall.

A gambrel attic roof combines both: the steep lower rafters are purlin-supported and the shallow upper ones are tied. Houses with a living attic are covered on the houses with an attic page. On large spans, over garages and commercial halls, we use steel trusses instead of timber.

Wall plate and seismic ring beam

The wall plate is a timber beam along the top of the wall that takes the lower ends of the rafters. In a seismic zone it cannot simply be laid on the masonry. We fix it to the reinforced concrete ring beam with anchor studs cast in during concreting, with a damp-proof layer between concrete and timber. Rafters are fixed to the wall plate with steel angles and brackets, not nails alone: in a tremor a nailed connection pulls out. How the beam itself is made and where the cast-in fixings go is described on the reinforcement and ring beams page.

Timber and its protection

We make rafters from kiln-dried softwood. Green timber, often sold cheaper at markets, dries out on the roof and warps: rafters twist, the ridge goes wavy and the covering screws work loose. We check moisture content with a meter when the batch is delivered.

All timber is treated with a fire and bio protection product before installation, with cut ends and notches treated separately. In Batumi's humid climate untreated boards at the eaves are attacked by fungus within a few years, and wood-boring beetles like dry lofts. Before the membrane goes on, we photograph the connections and the treated timber.

Connections we build to the drawing

• ridge connection with plates or a purlin, with no gaps between rafters;
• rafter seat on the wall plate notched no more than a third of the section, with an angle;
• ties and collars bolted, not nailed;
• struts and posts bearing on a load-bearing wall, not on the floor mid-span;
• sprockets for wide overhangs against driving rain;
• trimming of openings for roof windows and the chimney.

If there will be a living attic under the roof, the rafter depth is agreed in advance with the insulation thickness and ventilation gap: a shallow rafter will not take the required layer; the layers are covered on the roof insulation page. Which covering goes on top and how much it weighs is decided together with the pitched roof.

How much roof framing costs

A rafter system in treated timber with fixings and materials costs from 135 ₾ per m² of slope. If you supply the timber, the work starts from 54 ₾ per m². A continuous OSB deck with underlay as a separate line starts from 57 ₾ per m², and eaves soffits from 81 ₾ per linear metre. A turnkey attic roof with rafters, insulation and covering costs from 400 ₾ per m² of slope. The final price is set from the design and the agreed estimate.