The Cabin

5. Rafters & Roof

construction drawing

5.1 Rafters

This building uses only 2 x 3 timbers for the rafters, but these are adequate when you consider that most houses with concrete tiles only use 2 x 4. Also, cedar shingles are considerably lighter than concrete or clay.

The Rafters were notched over the head plate and screwed through into the plate. The top end was fixed to a hip board as shown above. I made a lot of mistakes with the angles when cutting the first few rafters, but eventually I cracked it and the roof structure came together pretty quickly.

5.2 Cross ties

At this point, when the rafters were in place, but before the breather membrane went in, I fitted three sturdy cross ties (See photo on previous page), each 2 x 6 inches (50 x 150mm) These were planed-all-round timbers as they would form part of the interior finish.

These ties served several functions: First they help stop the roof spreading and pushing the walls outwards. Secondly, they will act as beams that take the weight of the sleeping platform and storage areas, hence the need for some beefy dimensions.

The ties sit on top of the head plates (wall plates) and are screwed into an adjacent rafter at each end as shown in the construction diagram above.

The ties divide the space roughly into thirds as shown in this plan view. Joists between the ties provide the support for floors on each platform but also for ceilings for the spaces below them, including in the porch area.

5.3 Breather membrane

Once all the rafters and the ties were in place the whole structure was wrapped in a breather membrane. This was stapled to the rafters, posts and stud work. Where sections joined lots of overlap ensured continuity in protection. When this was completed the building suddenly felt past the half-way point. This is more a product of psychology rather than any rational estimation of project schedule, but once enclosed with the membrane it certainly felt like it was a building and from now on It was just a (very long) process of finishing.

5.4 Roof

The first stage in the roof work is to screw tile battens to the rafters. My rafters were spaced at approx 15in (400mm) centres. (Above left)

Next, horizontal battens are screwed at right angles to the these. (Picture above right). The spacing of the battens needs to be set depending on the pitch of your roof. For roofs between 22°-89° battens should be spaced at 5 in (125mm) centres, which is equivalent to 8 battens per metre. This means each visible ‘row’ of tiles will wave 5in of tile visible below the tile above. For details on how to fix the cedar shingles here is a video from John Brash — the company from who my shingles came.

Cedar shingles are very easy to work with, but care is needed as mistakes are difficult to remedy. Study the literature before you undertake any work. When the shingles are laid correctly, at every point on the roof there are three layers of shingle. As you nail each row the nail passes through two or three layers, and the next course of shingles covers up all the nails. You have to use special nails for the job – normal steel nails will lead to streaks stains due to reactions between the nail and chemicals in the timber. The first (lowest) course of shingles needs special treatment to ensure watertightness and a correct profile to the roof, plus a suitable overhand to meet the gutter. I won’t try and give all the details here, but here is good video to get you thinking:

This one is good too

Finally, special ridge tiles are available to cover the ridges and make the roof look top-notch.

Cedar Shingles age very gracefully, turning grey and accumulating some lichen, but in 15 years they have never failed me and I have not had any problems with them. The only maintenance is to remove any leaves that build up – for example by cleaning out blocked gutters – as if tiles remain permanently wet I imagine they would decay more quickly.

Here are some images showing how they have aged:

  1. Introduction
  2. Design Considerations
  3. Foundations, Posts and Floor Joists
  4. Walls and Windows
  5. Rafters and Roof
  6. Cladding and Finishing
  7. How it Looks Today (15 years on)

Leave a Reply

%d bloggers like this: