More north wing trusses

The north wing currently has 8 trusses installed, right up against the east wing roof. Our first job is to get as many of the remaining ones up as we can. Ric had prepared the trusses, cutting the birdsmouths that will bear on the wallplates and trimming the rafters roughly to length. We mortared 22x100mm wallplate onto the outer edge of the two courses of 215mm concrete blocks that make up the top of the wallhead, using 1:6 cement mortar. After it had gone off, we drilled and screwed it into the wallhead, 4 screws per 4.8m length.

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The following day, we marked up the positions of all trusses that we could (we have not yet built up the wall around the front door). We then used the angle grinder and medium breaker to cut notches in the concrete blocks below the top two courses of blocks. These are in the way because we have cut birdsmouths in the rafters, dropping the lower edge of the rafters too far for the design of the wallhead.

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We then got down to placing trusses on the wallhead, without Ric to guide us. He had parked them just where we needed them, we could hoist a truss at a time using our mobile bay of scaffold, push the truss over the wallheads and stack them up in groups (six in this case), to keep enough space to work in. We could then shuffle them along the wallhead away from the installed trusses, dropping the last one into position and using batten nailed to the top collar to hold the truss in place. We repeated until all had been nailed in place.

We checked the alignment of trusses against the north wall wallhead and also checked that the upright timbers above the collars lined up. We put a truss clip under each end of each truss, then strapped every second truss down to the top of the wall. After two days we had 12 trusses up, joining the existing 8. This is just over half, with 19 left in total, but 11 that we can install until the front door is built up. When I ordered the trusses, I was down south and did not have accurate measurements of the length of the north wing, I erred on the side of caution and ordered 41 trusses. So we have two spare trusses. Ideas on a postcard, please…

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More roof!

Ric stayed on after we headed south and concentrated on the roof over the east and north wings.

He got 6 more of the raised-tie trusses in place on the north wing next to the two we got in place just before we left. He had to puzzle out how to a) trim the ties and cut the birds mouths, b) hoist the trusses over the wall and c) get it placed on the wall. Entirely on his own and in a reasonably efficient manner. The first one took a couple of hours, the following 5 took 20 minutes each. He ran out of wallhead and turned to sarking boards.

We had moved one of the bales of 192 sarking boards round from where Ellon Timber had dropped them off, to a convenient place outside the east wing. They had been treated just before we got them, they were really quite wet and weighed a ton. Even with three of us it was miserable job. So, unsurprisingly, Ric had extra work to do to lug the boards up onto the trusses in order to fit them. He started at the bottom and worked up the east side of the east wing trusses.

He attached the rest of the fascia board and positioned it so that the lowest sarking board rested on the top of the fascia, lifting it up into a small ‘kick’. We will need this later on to accomodate the thinning of the slates at the botton of the roof, from two overlaps per slate down to just the top slate and the half slate underneath. He used a guaging trowel to form the required 2mm gap between sarking boards, but did point out that as they were saturated, they could not expand more that they were at the moment. When they do dry out, the gap will probably be bigger. Initially he just stacked the boards up the roof and quickly found he was having trouble getting usable access to get higher boards. So he decided to measure the boards out, but not nail every 5th board, which he took out temporarily to give himself footholds. Due to the irregular placing of the east wing trusses, through the need to accomodate the stair well, escape window and the jack rafters over the gallery area, he spent quite a bit of time trimming the boards to length. He got about halfway up the east side of the roof and decided he needed a change.

He headed over to the west side and decided to sort out the join between the north and east trusses. So he got some of the sarking boards built up on the north wing trusses, then ran boards all the way across the stair well area on the east wing trusses. He attached a ridgeboard to the end-most north wing truss, across to the tiny triangle of truss provided by Stevenson & Kelly, then a short length of ridgeboard from the other side of the triangle, terminating against the east wing sarking. He put a jack rafter each side on the longer ridgeboard, again with the ends resting on the sarking boards. This extended the north wing roof up the slope of the east wing roof. Ric trimmed sarking boards and laid them over the framework to define the valleys. He laid the rest of the sarking boards on the west face of the east wing roof, right up to each end, extending the boards over the inner edge of the gable walls.

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On the north side we have a short length of fascia that runs alongs the east wing truss ends until it joins the valley between the rooves. We had calculated that the space below this fascia, down to the north wing roof, would be within the thickness of the wall at that point. On the old roof, the rafters were trimmed off at the wallhead, so the equivalend triangular space was bigger and was OK because there was internal rubble wall to protect from the weather. We got something wrong, though, because for some reason, there is a small triangular hole where the internal wall used to be. This is irritating, but we will fit some treated timber across the hole and it will be behind lead flashing.

On the south side, we of course have a much longer length of fascia but we have the same little wedge of empty space to fill.

There is loads to do on the roof next spring, but getting most of the roof boarded is a real milestone!

Roof trusses delivered

Stevenson & Kelly had been a bit uncertain about actual delivery dates and in fact they came a day later than we expected. They did all arrive on the same day, though, where I was expecting one load one day and the other the next working day. We had a similar level of nervousness ahead of time as we did before the cement trucks arrived for pouring the slabs – the whole thing had the possibilities of being a complete nightmare, given we will have to manhandle the trusses off the truck, we do not have a fork lift or teleporter.

First load: So I got a text from the driver saying they were setting out and sure enough, 40 minutes later I spotted the tops of trusses heading over the skyline. I phoned the driver and pointed him in the right direction. He had our 41 raised-tie trusses for the north wing. To get the first half unloaded, he drove in forwards, stopping halfway along the north wall of the steading. The driver was really helpful. He kept the trusses on the truck tied at one end, released the outermost truss only at other end, then did the same at the first end. Myself and Ric were able to pull the truss to the edge of the truck and lug it down. We lugged them over to the north wall and leaned them just about upright. We ended up putting them over a window opening that we need to build up, before we can get trusses on the north wing. This is a pain, but we otherwise had a bale of sarking boards exactly in the way and did not have time to move them. We got that half of the truck emptied, he turned round in the holiday let driveway and backed in. Then, more of the same. So after a couple of hours, the driver headed off for lunch and said he would be back in a couple of hours.

Which he was. He had the 23 attic trusses, all on one side of the truck, and drove in forwards again, right down to the hardstanding on the east side. The same procedure, but we minimised the lifting by resting the trusses against the east wall directly in lie with the truck. These trusses weigh a touch under 100kg and, by the end, we had just about had enough. The driver headed off happy and we celebrated with a good cup of tea, relieved that a) we had got the trusses off the truck and b) had not been squished doing so!

Trusses ordered!

With a bit of to-ing and fro-ing, we got the final quote for the trusses for north and east wings. We paid the money on the last day of August and left it to Stevenson & Kelly to work their magic. They agreed to deliver trusses for the Thursday after we get on site. This will give us time to do preparation and for Ric to get up.
We offered up a little prayer that they will fit!

Rethink on roof trusses

We need to order roof trusses now for the east and north wings, in time for September, and have changed our minds again. We will use attic trusses in our east and west wings, not the raised tie trusses the architect specified.

A quick history lesson: Our architect specified raised-tie trusses. The structural architect added extra bracing from each truss down onto the floor joists, because of the extra height we need in the upper floor. Reading around, this is because it is not practical to design trusses with the raised ties lifting the roof by more than a metre – where we need around 1.3m of extra height. Building Standards signed-off the modified design.
The truss designer said no and designed attic trusses. The architect had words with him and I thought he had relented and could design them.

However on further investigation, neither of our local truss manufacturers will design trusses that are not fully self-supporting, since they fear they would be blamed if they were installed as per the plans, but failed. I have some sympathy for them, but it left us in a bit of a bind. So we have just had a mad scramble to come up with attic trusses that work – without being able to get onsite to check & confirm measurements.

The least disruptive solution, for us, looks to be where:

1. The attic trusses bear on the wallheads, rather than be supported on timberwork underneath. So the timbers that form the attic walls and floor will hang down between the steading walls. We need studwork underneath anyway, to hold our wall insulation, and we can brace the trusses against them. But if they also had to bear the weight of the roof, we would a) have to go back to the structural engineer to check whether the thickened floor slab was sufficient foundation and b) would need 200mm lintels across our pre-existing external doorways, lifting the ceiling by that amount. This would be very bad for the attic room.
2. We allow 80mm gaps between the steading walls and the truss timbers, both sides, because the walls are not flat. I took 7 measurements between the walls at different heights and they generally slope outwards as they go up. The west wall also has a measurable bend outwards along its length. However, at least one piece of our concrete blockwork on both walls sticks proud of the rubble by up to 60mm. I really do not want to be trimming the blockwork and any stray lumps and bumps of granite just to squeeze the trusses in place. The earlier truss design gave us a comfortable 3.6m of width in the attic room.
3. We use 150mm solid foam roof insulation, in place of the specified 280mm frametherm panels, because the rafters cannot be more than 220mm deep and we must have a 50mm air gap above the insulation. The strength grade of timber used for trusses, T26 (or TR26) does not come bigger than 47 x 220mm and the truss designers really are not interested in composite rafters i.e. two lengths of timber, one on top of the other. This saves us the cost of extra timber on the trusses, but the premium on the insulation probably outweighs this: We will have to go for higher spec insulation, with a lambda value of 0.018 rather than the usual 0.022. The equivalent value for the frametherm is 0.032.

The one advantage of attic trusses, for us, is that it will be easier to support the trusses over the gap where the north wing joins the east wing. The foundation is inside of the line of the wallheads and we had worried about making sure that the raised tie trusses took this into account. Instead, with the 80mm airgap, we can simply support the trusses from underneath.

And we do not need to change the design of the trusses on the north wing. They stay as raised tie trusses, because the bottom chord (top collar) is low enough to keep them stable.

We now wait to see if what we have asked for is possible. And I will be chewing my finger nails until I know that my measurements are right and the trusses fit properly. We really do not want to be rebuilding our walls to fit the trusses!

Meanwhile, here is an earlier incarnation of our attic trusses…

And here is the equivalent rasied tie truss, for the north wing…