MortarThePoint

Yes the bottom chord forms the ceiling for below. I calculated the load on the left hand mount (490N = 49kgf) by balancing the moments about the right hand mount. Balancing the overall forces gives the load on the right hand mount (wallplate) as 314N + 689N + 515N - 490N = 1028N = 103kgf (or about 1400N if I add a tank). Intuitively this makes sense as the largest force involved is that of the tiled roof part. I have only involved the truss designer on this, not the SEng. The wall is 4.8m long cavity wall and continues up a storey. As far as I can tell, such a restraint straps serves to limit the possibility of the of the joist and the wall separating as shown by my red arrows on the image at the very bottom of this post. The lag bolts would resist a ledger board pulling away from the wall and then the joist would have to be strapped to the ledger board. https://www.labc.co.uk/news/how-get-it-right-supporting-joists-external-walls

Thank, prettier drawings by hand than my computer ones, but my hand drawing skills are bettered by my 5yo. The left hand mounting load of each truss is around 490N (49kgf). There are 7 trusses so that totals 3.5kN (350kgf). If I add a tank (dotted red) to this roof space as I am considering, it would up the total load by about 65% to 5.8kN (580kgf). If using a ledger board and lag bolts at average 300mm centres that would equate to around 16 bolts so 360N (36kgf) per lag bolt. Does that sound scary? Truss mount load on left calc: Flat roof part: Fo = 1.719m*0.6m*13kg/m2*10N/kg = 134N Mo = (1.481m+0.5*1.719m)*134N = 314Nm Tiled roof part: Fb = 2.854m*0.6m*78kg/m2*10N/kg = 1336N Mb = 0.5*(1.481m - 0.450m)-1336N = 689Nm Truss selfweight: Fp = 22Kg*10N/kg = 220N Mp = (1.481m+0.5*1.719m)*220N = 515Nm (over estimate) Left hand mount: Mr = -(Mo+Mb+Mp) = -1518Nm Fr = Mr/3.1m = 490N (49kgf)

Thank you for the consideration and the diagram! I think it will only try to pull laterally if the top vertical left hand member in the diagram contacts the wall, which it doesn't. That vertical member is 25mm nominal from the wall so the only member contacting static points is the bottom chord at the wallplate (R) and at the hanger (L).

I don't see what you mean. tipping of the hanger side to side? There isn't a top mounting just bracing.

All that said, and here is a retrofit specifically for thin joint. Not relevant to me but thought I would add it for completeness:

Yes I'm going to go that way. I also saw that he NHBC says that masonry hangers shouldn't be cut "into the walling" I presume that means shouldn't be retro fit rather than saying it shouldn't be cut in to the block itself. Also, some other warranty providers stipulate that materials shouldn't be mixed in the area and I have a transition from blockwork to brickwork at this level. Just need to decide my ledger board size. At one end of it I am going to rest it on the wallplate of a perpendicular wall as well. If I had thought about t more, I could have built it in to the wall at the other end as well but that's not a big issue. https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-4-timber-and-concrete-upper-floors/6-4-13-joists-into-hangers/ https://9329f7a9-f105-4a46-b2bc-a658e29c21db.filesusr.com/ugd/981144_d12f36e2d1bb4fe78f9179e65dd7981f.pdf

Saberfix are a bit more optimistic about the SWL with their product. Seem hard to find for 38mm trusses/joists (Screwfix only sell the 50mm ones annoyingly).

Other than the cost and minimal effort involved I can't see a downside

Well stacks are pretty much finished now, 4 courses left on the smaller one. I think we have followed good practice in terms of chimney damp handling, but I like belt and braces so was wondering about applying StormDry since the scaffold is there and it will never be easier. For the main stack the area is 30 courses x 4.6m round + 1.2m2 flaunch = 11.6m2 Smaller stack ~4m2 It's not cheap stuff running at about £4/m2 (5m2/l and £20/l) but feels worth it the £60 to me. Has anyone used StormDry and has any comments? Does it affect the appearance of the masonry? Looks a bit strange when the rest of the wall is wet below, but that's just showing it's doing its job. Here are some interesting likes: General StormDry promo video: StormDry vapour test: StormDry watering can test: StormDry flood test: not really relevant but interesting:

Is that above a sink for good measure? ?

An advantage of the chipboard over larger sheets is that it is 2400 x 600 so I can lay it on my own.

I have two areas I am debating what to put down as the floor. One area is above the garage in a home office space and the second is in the attic trusses of the house. 22mm Caberdek P5 (~£6/m2), glued along joins and joists and screwed @ 150mm centres along joists 21mm softwood plywood (~£10/m2), glued along joins and joists and screwed @ 150mm centres along joists 21mm Redwood floorboards (~£10/m2), ?glued along joins and joists and screwed to joists? 21mm hardwood plywood ripped to planks (~£12/m2), glued and screwed to joists perhaps glued along joins. I've seen some nice results online that people have got with this. Particularly above the garage, a key advantage of the last two options is that they could be left bare as the finished floor. It may create an acoustic issue as carpets really help against that, but it could look good and be functional. A concern with Redwood floorboards is that they could be a bit soft and end up very dented. Is there a treatment that can be used to harden the top surface a bit. Trusses are on 600mm centres.

Lovely cat slide roof! There is a lot of roof area going into gutter (3). Being above the front door you definitely don't want this overflowing. I think @PeterW is right, you'll need a deepflow gutter to handle the intake. Worth also looking at square cross-section guttering as may work better with the aesthetic and it also has higher capacity. You'll need that velux to be very well fitted as I expect in downpours you'll have water approaching it from the valley.

If you haven't chosen your flue liner yet I'd suggest considering a 200mm one rather than the 175mm we went with. It doesn't cost more (liner sections tad bit more, but less granular fill around it) and allows more flexibility as to what is connected to it (e.g. could change to an open fire down the line).

Yes I think they work well. They provide a bit of interest and I think they do accentuate the corbelling.

Roof pitch is 48 degrees and your correct that pushes up the chimney. That said, the edge of flue liner to weathered surface horizontally is 2.7m, so well beyond the 2.3m minimum. That suggests we could have had it about half a metre lower. I guess it's just one of those things that when I looked at the architect's drawings it didn't occur to me to change it so it must have looked right. There may be some architect's wisdom I am lacking. One scaffold visit for the chimneys. The brickies didn't go up as far as I had hoped before the lift so they had to 'nose bleed' it to start with on the scaffold laying ~450mm below the boards.

No the pots go on last at the top ? Just kidding. The architect's drawing included a 450mm projection above flaunching. With 225mm of embedment, that left us either going with 600mm or 750mm as there are no 675mm pots of our type. In hindsight, I think we could have had just 150mm of embedment, but I'm happy with how it looks. Your design looks nice and I think suites the taller pot It may be a function of the aspect ratio of the chimney itself above the roof line.

Thanks. Do you like the approach of having it half lapped and half flush? Viewed from above, it means the tray has to be cut to this shaper where the green portion ends up embedded in brickwork and the orange portion sticks out to then get bend down over the flashing and back gully.

Thank you. It has been a challenge to get my head around. Haven't really focused on the cost so much as it feels like such an integral part of the house. The liner system was £1464 for two chimneys. Above roof level: the brickie spent about 4days 1:1 so that's another £1200 or so. Bricks above roof level were about 800+200=1000 so around £650. Blocks probably £150. Below roof level: the brickies probably sent 4 days 2:1.5 so that's about £2200. Extra bricks over being just wall probably around 400+700=1100 so around £700. Blocks probably around £250. Lintels around £250 (Naylor R9 £93 and Supreme R21?£130?). Extra footings probably around 7m3 so around £850. Probably additional truss cost of around £150. Total: £7864 so call it £8k So that's £4k per chimney before even connecting a stove to it. Probably looking at £5-6k all finished.

Well the main chimney is finished, then had to rush to try and save the flaunching from some rain which has resulted in some minor damage. A shame, but I guess you seldom see the top of a chimneys flaunching and it's more important that it is weatherproof. Here's a photo after I enacted a repair (approx. 3 hours after the rest of the flaunching was finished and in the half light). The perspective of the photo makes the pot look massively off centre, but it is in the centre. The second chimney is up to the level of the second lead tray. The tray is placed on to protect the brickwork from any rain before it's finished. I'm still liking the hybrid approach of having the tray sticking out around the back and part of the sides (shown red) and folded down over the flashing. Round the front and part of the sides cut back to flush with brickwork.

Is there anything wrong with using the tray to form the cover flashing? There may not be enough lead to reach down 150mm though, probably just 75mm. This is from the LABC technical manual and looks to be showing the tray forming the cover flashing: I wondering is @PeterW knows if this is OK or if the top flange of the cover flashing can be tucked into the same bed as a tray.

Have you had to work this out for your chimney @epsilonGreedy

I'm getting confused about the second lead tray on the other chimney now which is going in tomorrow. I have had both trays made large enough to extend out of the brickwork and lap up or down the brickwork by 75mm. I definitely need that for the first tray that is mostly within the roof space. On three sides of the chimney, that first tray will be lapped up the brickwork and on the fourth side it will lap down the brickwork. That puts the apron a brick course below the last bit of stepped flashing on the sides of the chimney. I've convinced myself somehow that the second tray is supposed to lap down the outside of the brickwork. However I have seen various diagrams online that seem to show it stopping at the edge of brickwork so not actually coming out and lapping onto the outer surface of the brickwork at all. Which is correct? I have drawn the two options below as viewed from the side of the chimney. It's a bit difficult to tuck the lead flashing in below the tray in the right hand approach. I guess the tray could come out wherever the flashing meets it, highlighted red here:

Thanks, I use two cheap tools QCAD and PowerPoint. Very different to the day job, but useful to convey the details. Yes, as conceived the pot is embedded by minimum 225mm. This is embedded 150mm in the cut blocks and mortar ('A'). Most of this is below the upper layers of slate though so will hopefully not get too moist.

It is on the outside. My second image probably wasn't put into context well. It's a closer look like this: