Slating the roof valleys

We worked our way across the second half of the east wing roof until we got to the point where the north wing roof meets it – this was the first of our roof valleys. We dug out the GRP valley boards we acquired several months ago and got to work. We peeled back the roof membrane from both sides, revealing the strip of membrane we ran down the valley for 500mm each side, it was intact and in excellent condition. We nailed the outside edge of the valley to the sarking in four places each side above the strip of membrane, ran double-sided butyl tape all the way up each side on the outermost of the two small ridges, stuck the roof membrane to the tape and trimmed it back to the ridge, leaving the second ridge and the full width of the valley open. We added a second length of valley trough above the first, overlapping by 150mm, and cut it to a mitre at the top to fit flush against the ridge of the north wing roof.

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We made up a wooden board to go down the valley. Using a length of 2 x 6, we trimmed it down to 125mm wide, then planed bevels on the underside so that it rested on both sides of the valley. We could slate up to the board to get a neat edge, we screwed bits of batten across at intervals so we could use it to get up and down the valley.

We dusted off one of our home-made wooden roof ladders and fixed it in place opposite the side we need to slate up. With this, our aluminium ladders, we had pretty good access to the whole area of roof above the valley boards.

I boarded the gap between the scaffolding platform and the north wing roof with a 50mm timber platform resting on a timber screwed into the sarking, this meant we could place ladders right up to the bottom of the valley and had easy access to the valley board and wooden ladder.

And so so to work. We found YouTube clips showing valley troughs being installed, including neat ways to mark up slates to fit the valley. This involved turning the slate face down across the gap between the slating and the valley board and marking the gap on the valley slate. We then rotated the slate so the long edge was against the valley board and marked the vertical line up the slate from the first mark. By cutting along this line with the slate guillotine, we produced exactly the right shape to fit against the valley board and nail into place. Coincidentally, the angle of the valley was just about the same as the diagonal slop of the slates, so most of the valley sales were very similar in size. We used slate-&-halves throughout, up to the top of the valley and transitioned to slates running across the top of the north wing ridge. The point where the valleys intersect with the east wing roof will need a lead saddle across it to protect the tops of the valleys, this needs both sides of both valleys to be slated up. Slating the other side of the valley was effectively exactly the same, but we used the other wooden ladder on the other side of the valley. This ladder rested on slates so we wrapped rolls of hessian burlap round the long lengths to spread the load and avoid cracking the slates it was in contact with. The end result was slating projecting neatly over the valley trough by 50mm and a 125mm open space above he valley board.

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Insulating the east wing

Whilst getting the roof weathertight has been a priority, we have been pushing on with insulating the timber studwork against our outside walls. The idea is to create a fully insulated shell inside the outer stone walls. So it must run from the insulated upstands at floor level, up through the studwork, through the floor joists, up the truss supports and rafters and across the top collar, to meet the insulation coming up from the other side.

Insulating downstairs
We ordered 30 panels of 140mm PIR panels and got going. We dug out our battered and rusty Stanley Jetsaw and, after a bit of experimentation, discovered a) that the panels needed cutting around 5mm smaller than the measured dimensions and b) that it is tricky getting nice cut edges exactly at 90 degrees from the facing. So the panels will push into spaces, sometimes with the help of a bit of timber and club hammer, but usually have some gaps that we filled with foam. The latter was very good at wedging looser panels into place. We made decent progress working round the downstairs walls, including up towards the roofline in the gallery area. We will leave the top of the gallery area until we can set up a scaffolding tower inside.

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Insulating upstairs
We pondered how best to work up past the downstairs studwork into the attic trusses. The floor joists of the trusses rest on the studwork and support the rafters with a web of upright timbers each side. This is 400mm deep and has two triangular spaces that will need at least partially filling with insulation to avoid thermal bridging. On the east side, the outside edge of the uprights align with the studwork, so we can run the insulation straight upwards, filling the outermost triangle with wedges of insulation cut down from our leftover 100mm insulation boards and halved (the trusses are 50mm thick). So the insulation will be adjacent to the stonework, with a 26cm void inside, where we run plasterboard over the inner upright. The west side is slightly different because the truss timbers are offset outwards relative to the studwork, by about 10cm, due to the outward lean of parts of the west wall.

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This is good for the rooflights. We placed them low enough to be able to see out of, so they are also recessed outwards beyond the line of the inside wall. We can run plasterboard back into the space between the trusses either side, to get more light into the rooms. If we choose to, we could use the voids in other places for recessed shelving.

Insulating the roof
For the bays between trusses that do not have rooflights, we are running the panels up between the joists to the bottoms of the rafters, then running panels up between the lower part of the rafters to the top collars, at which point there will be room to use 300mm of conventional loft insulation. The rafters are 220mm deep so the 140mm insulation board leaves an 80mm void above the insulation, which connects directly down to the soffits, so meeting the building standard for ventilated space below the sarking boards.

Insulating round the rooflights
We are running the insulation up towards the frame for 120 cm above the top of the downstairs studwork, with a separate piece above bevelled and sloping at 45 degrees outwards to the sarking boards immediately below the bottom of the rooflight frame. We run the insulation horizontally from above the frame out to the bottom of the rafters and continue up to the top collar with another bevelled panel. We cut a 180mm wide piece of 25mm insulation board across the diagonal down the length into two bevelled sections and fitted these either side of the frame down to the bottom of the rafters. We also put strips of our left-over 25mm insulation on the other side of the rafters from the frame, to reduce cold bridging from the void. We filled small gaps with foam. The escape window was treated in much the same way, but because one edge does not butt up to a rafter, we built up the timber to match the profile of the trusses. We also built batten into the space below the frame to support the weight of people should it ever be used in anger. We also want to build a seat under the window.

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Starting the second roof

We moved the scaffolding round the other side of the east wing and began all over again. It took a couple of days to work up to the ridge, slating one side of the first rooflight, at which point we had new things to do.

Flashing over the ridge
We had run the lead flashing up the first (east facing) roof and stopped just short of the top-most soaker. We did the same on the west-facing side, then made up one extra length of flashing which we planned  to run up one side, fold over at 90 degrees (technically 96 degrees) and run down the other side to lap over the existing flashing. I anticipated herding cats, but it worked really simply and well, with the skirt forming a neat double-fold below the apex and the beading making a sharp-ish about turn in the grooves, where they intersected. I got it mortared over and left it to go off before the next step…

The top courses of slate
I calculated how to finish the roof up to the ridge, to be weatherproof. I was able to run another full course of slates that brought the top edge just about to 120mm from the ridge, this is just about where the bottom edge of the ridge tiles will sit. So I could fit a 260mm-height course at the 190mm spacing, nailing them in just above the course below and leaving room to nail a 130mm row above that, giving proper overlaps. If the roof is not quite fixed height, I can adjust the last two courses accordingly. I had to use the 45mm roof nails in place of the 38mm I used on the rest of the roof, because there were three rows of nails in a compressed space and they had to accommodate three full thicknesses of slate. Of course we had to do both sides of the roof, using our  23cm wide slates on the east side and the 26cm slates on the west.

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Fitting the (first two) ridge tiles
Ric advised us to fit the ridge tiles at the end of the working day, so we did not disturb them with hammering. The first one needed to flash into the lead flashing I had run over the ridge. I carefully peeled the fold in the skirt and pulled it out and up, to give room to fit a lead soaker behind it. This followed the profile of the ridge tile. Folding it without tearing it was a challenge!

Next we mixed a bucket of 1:2 lime mortar, slathered it either side of the apex, keeping the exposed membrane clear and slid the first ridge tile in under the soaker. I left the lead unfinished until the mortar had gone off. We had room to fit a second ridge tile in against the first, using a sprit level to get them lined up and finished. The following day, we formed the lead soaker over the profile of the ridge tile and pushed the lead skirt as far back in as it would go.

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Finishing the first roof

Slating up to the lower corner of the roof
We started the roof against the extension of the gable wall. This originally allowed large doors to open back over the opening that is becoming our big window. All the other corners end above our runs of facia boards, which project outside the building line – a consequence of lifting the roof by 45cm without building the stonework with it. So whilst most of the edges of the roof will be against coping stone, the bottom edges come past the padstones into open space. We handled this by projecting slates on the corners 50mm outwards as well as downwards. This involved quite a bit of cutting, plus we fixed the slates using A2 stainless screws to avoid stressing the fascia support by whacking roof nails in. The end-result was pretty good because it was neat, solid, but also unobtrusive.

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Slating round a soil vent pipe
We have three openings to make in the roof (two more if we install the MVHR). We have soil vent pipes above the east and west upstairs en-suites and a stovepipe in the north wing. The east wing soil pipe follows a circuitous route into the family bathroom from the inspection chamber outside, diagonally across the adjacent bedroom, up to the en-suite in what will be the wardrobe for the ground-floor bedroom, across the gable wall of the en-suite, then a dogs leg across until it is directly above where it entered the building, in what be another wardrobe (for the upstairs bedroom) and finally upwards and through the roof. The soil pipe in the west wing en-suite is handled similarly, our other soil pipe is all downstairs and we can get away with air-admittance valves to vent them.

We decided on old-fashioned lead slates for the SVPs, with the soil pipe projecting upwards through it by 600mm or so. We got a pair with the pipe opening at 45 degrees, near enough for our 42 degree slope. We cut away a short section of one sarking board and a sliver off the one immediately below it, to make a hole loose enough not to restrict soil pipe. We then spent a merry couple of hours cutting slates to fit around the upstand and flashing the lead slate in to be fully watertight. I added extra lead below it, fixed with double sided butyl tape, to give a good enough overlap onto the slates below. We left the upstand without pipe in it until we get round to doing our soil pipe – not far away now.

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Finishing off
We slated onwards and upwards, flashed lead over the soakers and mortared the lead in. Apart from the very top rows, which we will slate from the other side, that was the roof fully sorted and ready for guttering.

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