PeterW

Why are ducts specified..? Is this for Radon..? Ducts are normally only used in suspended timber floors to ensure there is airflow to stop damp causing issues with the timber

Fermacell is not for the faint hearted as it’s a very different product to plasterboard. The green PB in @Onoff photos is moisture resistant PB, bit more expensive than normal PB but great for kitchens and bathrooms. Still needs a skim though.

If you void the chimney then it needs water egress points and also a cavity tray. I would cap the pots off with proprietary caps and then weeps at the bottom. Fumes can’t get into the chimney itself as a balanced flue has to be gas tight !

Wall ties and structural ties are two different things. I’d want some metalwork set into the brick work every metre thats screwed back to the frame with something decent. The loading on a chimney that can potentially twist is much higher than a flat wall.

Buy the bits in SFix..! 3 pack of T30 is £2.59

You will still need a lintel over the opening yes, but you can also tie in the chimney with some metalwork as you go as it’s not exactly something you want swaying in the wind ....

Have you actually priced up - or checked availability of Celcon HS Foundation Blocks ..?? H+H Celcon HI-7 Aerated Concrete Block 440mm x 215mm x 300mm 7.3N Pack 30 £6.17 EA Availabilty - to order (2-4 weeks) That’s straight off my trade pricing page with one of the big BMs Solid Dense 7.3N Concrete Block 100mm Pack 100 £0.87 EA Availabilty - in stock So that’s available on site on Thursday. Pays your money, takes your choice.

Lightweights are for standard builds - not B&B - so don’t have to be as strong as the load they are bearing isn’t concentrated on the edge of the block. I’d suggest a chat with an SE who should be advising on this sort of thing would pay dividends.

Cost of flue liners, adhesive and vermiculite fill would be £1000 or so plus labour to install. Chimney can be built as a fake chimney with the pot(s) on top and sealed off so they are decorative. Quick and easy, just needs a cavity tray near the bottom with a couple of weeps.

Conventional Flue is mad ..! It’s 12% less efficient and £1000 more expensive ..! Balanced flue out the back as what nick said and then insulate the box. You don’t need a liner for the BF

Decent stainless gas liner with correct closure and hanger etc will be £300 plus, and then the GSR has to install the liner as it becomes part of the installation so scaffold needs to remain. So add £250 plus scaff costs for fitting ... Built concrete liners with the correct sealant between are exempt as they are deemed structural so do not require an inspection by GSR. But my money would be to spend on a balanced flue gas fired log burner. Something like the Gazco Huntingdon 40 would fit perfectly and it can be routed up above the inner lintel so it “looks” like a proper stove and then out the back of the chimney breast and you will never notice it.

You have to fill the below ground cavity for strength - either rigid insulation or weak concrete mix - so is saving you nothing really.

If the pour is that flat then well done as they can appear flat but aren’t level...! So are you going with thermaline or PIR on the inside then ..? 100mm Rockwool on its own won’t meet building regs now.

No because you need to start from the foundations at the correct cavity width. To meet regs from memory you will need 125mm of bead unless you line with PIR or thermaboard, The thermal difference of “thermal” blocks vs ordinary is negligible anyway, and they cause more problems than they solve when it comes to internal finishing and hanging things etc, not to mention they are about 60% more expensive than standard 4N blocks.

What is your wall cavity build up ..?? Is it 100/100/100 or have you got a wider cavity ..? As @Russell griffiths alluded to, trenchblocks are the devil and a pig to work with. As the first course they will need to muck up the corners etc anyway or split where the rounds are high so make it easy and use standard 7N concrete blocks underground.

Yes to meet building regulations. Can only be used externally or where each joint can be inspected (comes in up to 2m lengths) so can’t be built into masonry Thats for re-lining old chimneys - you would still need to build the stack and pay £3-400 for a decent liner I’d buy a very good carbon monoxide alarm and put it in the room as that a is a recipe for killing someone. I would give serious thought to making the chimney decorative and using a gas stove with a through wall terminal as was previously suggested

Check your SE spec but everything below the beams should be 7N. What’s your cavity / fill..?

Those are very detailed and clear.

Is that warranty from a point where there is a build that’s been started ..?

Only real option is pull down that external skin and move it out to give you 100mm cavity. Then full fill the cavity with rock wool and wrap it past the edges of the block onto the TF. What chimney system are you using ..?

So how are you insulating that cavity ..? otherwise you have a monumental cold bridge through that corner.

I’ve added short cable lengths to stuff like these and just Wago the ends. Easier to make up on the bench then push into the ceiling space.

Back to back them but swap them right to left so one WC is before the other. Make the wall 200 wide but make it from H frames with the 4x2 on edge and join them with OSB gussets. Soil goes down the middle with 45 branches angled out to introduce the “contents” and the basins provide additional flow. Showers under the floor in 50mm to hit the stack further down.

Unit does. How much frame is showing..?

If you are doing it properly then all the plaster comes off and you start from bare walls. Its retrofit then it’s as best you can get. Is it a double glazed window ..??