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.
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!
The moment of truth approached. I had specified the dimensions of the attic trusses without being on-site to check them. I had a nagging worry that we might have to butcher a lot of concrete blockwork and wall to get them to fit.
Moving the trusses: We worked out a sensible way of moving the trusses one-at-a-time inside the east wing. We used our battered, but just about serviceable, sack trolley at the front of the truss and our stone trolley at the back. Ric screwed a length of batten to the top of the truss and was in charge of keeping it upright as we moved the truss. We wheeled the truss round to our big window, lined it up and pulled it up over the foundation blockwork on scaffold boards. As we got closer to the concrete lintel, Ric leaned the truss down to a 45 degree angle until the top of the truss just rested inside the window opening. There was not a lot of spare room, but we were able to jiffle the base of the truss further inside, then pull the whole thing through as Ric pushed the truss upright again. We shuffled the truss fully inside, then were ready to go.
Lifting the trusses: We added an extra set of uprights to the scaffold tower and put the hoist as high up it as we could. Ric tied a beam across the lifting points on each truss and I hoisted the truss off the ground. With a little care, we were able to swing the ends of the rafters over the wallplates, then we pushed the scaffolding right along to the north gable wall.
The flavours of trusses: Most of the 23 trusses are simple attic trusses, designated T2 by Stevenson & Kelly. The stair well requires two T4 trusses that are of similar construction as the T2s, but have a shorter length of floor joist on the stair well side, that rests on the timber framing at the back of the well – effectively leaving a hole in the floor so the top half of the stairs can come up and rest against the shortened joists. The rafter on that side is also shortened and there is a temporary timber down to the shortened joist, to hold it together. The space where the rafter has been removed is immediately below where the north wing roof diminishes against the east wing, so I expect we need to run sarking boards over and insulate from above. The T4 trusses have pairs of T3 trusses either side of them, to brace the overall structure, they appear to be identical to the T2 trusses. Further down the roof, we have one T5 truss which is again based on the T2 profile. It has a full-length floor joist and rafters, but one side is missing the supporting timber work and is held together by a temporary timber. We will trim the rafter this side to fit our emergency escape window in. This is to be a 90cm x 160cm roof light that will rest on the wallhead and allow us to get out if the stairs cannot be used. This has doubled-up T2 trusses either side, to brace it. Finally, at the end of our run of trusses, we have a doubled-up pair of T2 trusses that will overlook our gallery area. Many of the truss spacings are at 60mm centres, quite a few are not and we have the length of structural timberwork on one side, so the roof was not simple to install.
T2 truss design
T3 truss design
T4 truss design
T5 truss design
The first trusses: We perched the first T2 truss on the end of the structural studwork on one side and on the wallhead on the other side, trimming the concrete blockwork to let the truss bear on the wallplate. We fastened the truss in place at either end with metal strapping and fixed three angle brackets between the top collar and the wall, to get the required 50mm centres. And that was the first truss in place. Our measurements were all good, it fitted and was level. The ceiling heights upstairs and down were good and there was enough room above the top of the window in the gable end to fit a sensible ceiling in. A relative triumph!
We had two more single trusses of the same type to fit, at 600mm centres. We did so, stabilising the tops of the trusses with two lengths of batten into either side of the top of the collars, measuring to make sure the distances matched those at wallplates. In fact the first struss was leaning a degree or two towards the gable, we adjusted the spacing at the collar to make sure the rest were vertical.
Stair trusses: Things got a little more complicated. We needed to fit a double T3 truss, then two cut-down T4 trusses that form the top of our stair well, then a second pair of T3 trusses. The cut-down trusses have just enough floor joist to bear on the back of the studwork, leaving a void over the stairwell. We have a nailing schedule for the doubled trusses, with 8 large screws to run down the middles of the rafters, collar and top & bottom chords of the easi-joists. We will do those later when we have a more stable platform to work from, in the meantime, we put 90mm nails in the vertical timbers to hold the trusses together temporarily. We fitted three more single T2 trusses and this completed the run of trusses that were supported on the west side by the structural timber.
Escape window trusses: Life got a bit more tricky at this point as we moved to supporting the trusses on the west wall wallplate. The raised wallhead was straight, but the wall below bowed in, where our concrete blockwork had followed the line of the original wall. This would not have mattered in the case of raised-tie trusses because the floor joists would have been separate and supported only from below. Being attic trusses, where the floor joist is supported at each end by vertical timbers, the wall projected about 50mm too far at the wall corner. This diminished along the wall until, seven trusses later, the wall had bowed out and was wide enough anyway. So we got the angle grinder out and cut seven grooves down the wall to just below the bottom of the truss joists, and stapled DPC on the vertical truss timbers that slotted into the grooves. So we fitted a pair of T2 trusses, the single cut-down T5 truss where we will have our large roof light/escape window and a double T2 truss the other side.
The rest: Up to this point we had room to lift trusses on the scaffold frame, swing them round and push them into place. As we ran out of space we had to change tactics, loading the remaining seven T2 trusses against each other and temporarily tying them to the last double truss. We moved the scaffold back in 600mm hops, dragged the stack of unfitted trusses back to rest on the scaffold and placed the last one in its truss clips then nailed it down. We ran our batten above the stack and nailed each one to the batten as we got it placed. We repeated the same until we had just two left, which we fixed as a double. Very neat and surprisingly quick given the amount of shuffling.
This used up the attic trusses, the remaining length of roof is over our gallery area, which will be a void from floor to ceiling. We have a pair of ridge-boards and a set of loose jack rafters to complete the roof.
Securing the roof: As we went along, Ric attached 1000mm x 100mm twisted restraining straps to every second truss. We nailed the straps to the trusses with the same 30mm x 3mm twisted square section nails we used in the truss clips. We nailed battens at 45 degree angles over the rafters until we could get sarking boards on, these were enough to survive storm Ali that arrived halfway through!
Post Mortem: This all took up time, we had a lot of little delays along the way and it was much more complicated in detail that I had bargained for. It took the best part of a full working day for the three of us to get the trusses inside the east wing and four more working days to get the 23 trusses completed.
We had miscalculated the height of our studwork a little and had to cut channels into it with a router. We had to trim the grooves into the concrete blockwork on one length of west wall that we knew was going to be in the way. We had to cut chunks of concrete block along much of the east side wallhead to allow trusses to rest on the wallplates, but this was less severe than I had expected. The two wallheads proved to be straight and parallel despite the waviness of the west wall.
We had an issue with the two stair trusses – they did not fully align with the trusses either side and in fact we had to use a planer to trim the rafters before we could fit the sarking.
Verdict: Overall, we did an excellent job. The trusses line up really well and are level. The apex of the roof trusses point quite precisely towards the apex of the south gable end – we hadn’t used it as a guide marker as we put the trusses up.
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!
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!
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:
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.
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.
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…
East Byreleask Steading 