Hexagon Roof

Yesterday Dan, Greg and I began construction on a hexagon end roof. To start off we measured the height, from the floor up to the top edge of the ridge board, which came to 2360mm. From this we made one plate at a length of 4720mm (twice the length of the height), which gave us the half span either side of the ridge centre line. The half span equalled the height because we decided to again do a 45 degree pitch roof as it saved alot of space in the small work area we had.

Then we came out from the edge of the ridge, running with the ridge, out 2360mm. From this we had a rectangle with sides 4720 and 2360.

As we had already determined from our experience with the truncated hip, when you put a plate 45 degrees across the corner of a plate and bring it in, the two new angles created are 135 degrees.

The above diagram then demonstrates how we figured out how to get even length sides ( B ) from our knowledge of the half span ( 2360 ) and its corresponding Tan angle of 67.5 degrees.

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Dorma Window Framing and Truncated Hips

Yesterday we finalised our construction of our dorma window. Dorma windows may seem rather simple but they require a hell of a lot of trimming and extra fiddly additions to make it stable and work properly. First of all we determined the overall height of the roof, then roughly how high we wanted the window to be. There wasn't any real limitations on this so we concluded that the top of the window should be about head height as it would be aesthetically pleasing. I then worked out the height of the small roof that would sit above the dorma window frame, 450(halfspan) which equals the height from the plate, then add 90mm (the height of the birdsmouth). The overall roof height was 540mm. Dan and I decided to start the dorma roof 300mm down from the top of the main roof and in the diagram on the previous post you can see that we also set the bottom back 300mm too, to make it look even.

To work out the height of the studs we were going to use we simply did the following simple subtraction equation, 2490 - 540 - 300 - 35 - 35 = 1580mm. We then cut all of our studs out of 90 x 35 to a length of 1580. We shot the studs into the bottom plate so that the last stud on the inside of the roof met up with its edge aligned with the underside of the rafter, this is so that everything met up nicely so it could be lined properly. After this we levelled our front and back studs and nailed them sideways into the rafters so that they remained level. Once this was done we measured some top plates to sit ontop of the studs and tie them all together. When the top plate was nailed on it tied everything together and provided our main part of the dorma window. We could then add our dorma roof and other trimmers to it.

The above picture shows our completed dorma window frame. The dorma window roof is 540mm high from the top plate of the dorma stud walls. The vertical studs are 1580mm high.

The photo above depicts our stud wall going back with the rake of the roof. As the roof was a 45 degree pitch the angled trimmer and the shortened stud were cut with 45 degree cuts. Later we concurred that we should have put an extra stud directly alongside the last whole length stud because it is a more important structural piece.

The picture above shows the actual side elevation view of our dorma window frame. It is a good contrast to the drawn up diagram in the previous blog post, where it shows some of the dimensions.

The picture on the top right shows the front of the dorma window. It has the two main rafters 900mm apart from each other with a horizontal fixing plate spanning between them. From this plate there is a small rafter that runs with the other main rafters, this way the roof can be sheeted and be structurally sound.

The picture on the left shows the valley of the dorma roof and its corresponding valley boards. The bottom of the valley board on the left is supported with a trimmer ontop of the plate.

The picture on the left shows the bottom plate for our truncated hip. A truncated hip is used when the wall plate has an angled section. The jack rafter for this truncated section continues down from the normal hip to the bottom plate. Two other hips, bisecting the angle of the wall plates, run up to meet the normal hip.

The picture above shows the following from left to right - centring rafter, left truncated hip, jack rafter, and the right truncated hip. The edge cuts on the truncated hips worked out to be 17.5 degrees, and logically the edge cut on the centring rafters and any creepers joining onto the truncated hips, worked out to be 17.5 degrees as well.

Dorma Window Construction

Today Dan and I continued on with our dorma window construction, which consisted of a 45 degree roof with an overall height of 2490 or 2455 not including the bottom plate. A 45 degree roof seemed rather simple in comparison to other pitches because the height always equals the half span of the roof. Because of this Dan and I thoroughly thought through each construction step and idea that came about so that we didn't overlook anything.

We constructed the main roof with the red roofing book as it was a fair bit easier to do so and building the dorma was the actual task, not the roof. One thing that both teams found annoying was that the edge cut for the rafters joining into the hips worked out to be 56 degrees but when we cut the rafters and tried to join them they were quite a significant amount out. So after some testing we just decided to simply go with a 45 degree edge cut, which fitted very nicely.

The diagram to the right shows the finished construction of the 45 degree roof that we had to work with. Notice that there is no jack rafter running up the middle to the crown end junction, this is so that the dorma window can be fitted easily. The two middle rafters are 900mm apart from one another, which was to be our dorma window opening. We used a 90mm birdsmouth cut, with the tail end totally removed. This provides a neat finish with no overhang.

Dan and I decided to put an opposing creeper to each side of the two middle creepers, so that they met up on the hip providing support to one another.

I enjoyed the construction of this 45 degree roof as i had always wondered what it would be like to make such a steeply pitched roof and i was wary of the ease at which things seemed to work. It was good to get even more practice at cutting rafters and hips without any supervision as i rarely cut them myself on the job site. Having two teams of 2 created a great rivalry between us and I enjoy the challenge of trying to build the roof faster than the other team.

Oblique end roof test

On friday we had to construct a small scale oblique end roof based on the brown paper drawing we had previously drawn up. Each of us had a different pitch, except for Dan and I because my drawing was out of square, it meant that my cuts wouldn't work properly. The pitch i was working at was 30 degrees. From the drawing we could align the bevel and then transfer the bevel onto the corresponding part of the roof, so for example you could get the hip bevel from the drawing and then use it to cut a hip.

We started off with a simple plate system of a roof that had an oblique end and then by using what we had learned about oblique roofs, marked out the half spans and also the positions of the long hip return and the short hip return, and finally on the end, the jack rafter position.

The short hip return (B) is exactly the same length as the Jack positioning (A).
First of all i cut the centring rafters and the other common rafters. I obtained their length by the simple equation of - (Halfspan / Cos(30)) - 12. For this i didn't want any overhang on my rafters so i made a 90mm birdsmouth, which would fit flush with the end of the plate.

Oblique Roofs

Over the past two days at Tafe we have been working on some advanced roofing booklets that Paul had handed out to each of us. So far in the booklets we have been learning about how to make precise cuts and measurements for oblique end roofs. An oblique end roof is a roof where there are two parallel walls but one stretches out further than the other, so the wall that joins between them is not at a 90 degree angle. Think of a parallelogram. The hips always bisect the angle of the two wall plates that it sits on, and the rafters are always perpendicular to the wall plate.

Where the short and long hips meet at the crown end junction with the ridge, the two hips are always 90 degrees apart. Because of this we can use pythagoras thereom to figure out other types of cuts on the expanded plumb cuts diagram. From the brown paper drawing we drew at Tafe, we can set bevels to all the different cuts nescessary such as the short hip plumb cut, long hip foot cut and the under purlin down cut.

By following the instructional booklet we received from paul, we made our own oblique roof cuts diagram with our own different pitch angle. I found this quite an involved drawing as you used previous triangles to help calculate the next triangle you were drawing in. One thing that was a bit difficult was that the triangles continually over lapped one another, so if you were to look at the finished diagram, it just looks like a jumble of triangles that don't mean anything. Other than this, the instructional booklet was very easy to follow and quite mind blowing because i always wondered how people worked out the underpurlin cuts and so on, and this diagram showed me one way of doing that.

After this we moved on to a calculations booklet where we had to find the lengths of the short hip and long hip and other parts of an oblique roof. All the different calculations stacking ontop of one another made it hard at times to concentrate on what you were actually trying to figure, because the length of one hypotenuse of a triangle was the length of an adjacent length you needed for another different triangle. I enjoyed these excersises because they were a logical challenge that i could work my way through. It also stretched my methods of using trigonometry too, which i consider the holy grail of roof carpentry because trig can solve most roofing problems.

One thing that was a real mind opener was learning that the square root of the (actual rafter length squared) + (the offset between the hip and rafter squared) = the actual length of the hip.