New porch.

Use 'Fibolite' blocks inside and out, above dpc.

These are also reasonably lightweight.

They are not prone to cracking and accept a rendered finish well, unlike celcon blocks.
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Looked into those, they are looking like the new choice, the shrinkage and less likely-hood to crack should mean a render that does not blow hopefully. The standard block size 440mm (L) x 215mm (H) x 100mm (W), will see if they are in smaller widths so internal space in porch is bigger.

Thanks for all the advice, have now started! Concrete/old canopy is down and started the trenches. Was going to lay them in a day, but realistically not sure if I could so looking at getting it ready mixed, a quote today was £75 more than the materials to do. So very tempting, what grade of concrete is best? C10 or go higher?

Went for GEN 3, all well!

But at the point of using wall starters and a little confused. I know they have to start above the DPC, one for each skin (double skin porch), using fibolite blocks so a tie in every block added. But how do you weather seal behind the starter? I assume you dont use a DPM, then read a vertical DPM is needed between the skins, can you use a cavity closer of sorts, and a seal is needed on the outside skin joing the house wall.

Sorry about the questions, but very keen to know and do a good job.

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About to put the DPM in along the block work and now considering how to return the inner skin to the outer for windows and doors. Cavity closers do seem the easier method of slotting in, but is returning the block work to the outer skin offer better options for flitting doors and windows?

How about the options for the bottom of the door.

Doing a quick budget is leading to cavity closers being cheaper too plus less hassle of hanging a dpm.
Proprietary cavity closers are expensive and can be fiddly to fit.

If i have enough cavities to fill, i buy a sheet of 100mm foil sandwich celotex, cut my own and foam 'em in.
Didnt think of that! Have one window and door. Cavity closer are about £15 for a 2.4m length.
My personal opinion of aerated blocks (Thermalite etc,.) are that they are rubbish, I would advise you to stay clear of them if you have the option. Yes on paper they maybe give a slightly better U value than standard blocks but in the real World I would rather have blocks that stick together properly and don't crack.

Have heard that! Well its started and the 7N fibolites have been used from foundations up. Have used a decent mix, blocks were damp and the work allowed to dry slowly. Hope it will stand the test of time!

Looking at going with kooltherm cavity closer by kingspan, seem pretty good, slot and require no return of block work.
I'm only basing my hate of aerated blocks on the Thermalites used on the inner leaf of my extension, given my time again I would have used standard concrete blocks, maybe the fibolites are a better block.

Good luck with your build :)
Stayed clear of those, did hear of the nightmares.

How far did you go into your houses damp proof membrane course for your build? Ive heard of 100mm overlap to just place it next to it? That is some difference. Getting the grinder out and going through it does seem dodgy!

grind out just above existing dpc and clear out the old mortar down to dpc lap new dpc over old and re point the joint, as for thermalite blocks i too used to suffer from 3d cracks when block work had dried and after numerous calls to manufacturers i was told it was due to the blocks having excess moisture in them when laid and using too stronger mix!! i now use a 5in1 gauge and i havent had a single crack appear since. as for moisture content of blocks they usually turn up on site with packaging full of condensation or from the bottom of the pile(soaking up rain like a sponge) so get them loaded out asap to start drying!!!! if your worried about the roof forcing your walls apart visit your local conservatory installer and see if you can buy a roof brace from them.
Heard about a strong mix causing problems. For the dpc grinding out a few cms seems logical and then having a 100mm overhang for the internal for the floor slab dpm.

The front door sits on top of the dpc, so where the floor slab dpm will join means a real lack of space even getting a bolster in will be a problem.

Been looking into hardcore for the floor slab, thinking of using concrete then the blind sand ready for the dpm. Have some ballast spare, but a reaction from chemical in the ground could cause damage (sulphates)?

Has anybody else done this method?

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