Please don't shout at me. I have tried reading up, but just don't get it.

[Big Jimbo]

I built a couple of houses for a client about 10 years ago. It was a brick and block build. People were scaremongering a bit and saying, oh, wait till you get to the Air test. I did a cement slurry coat on the inside of the blockwork. Ran a bead of silicone around the blockwork to floor screed. I put a load of silicone around the socket boxes before they were fitted and stuck silicone up the wall cappings where the wires came down. It was dot and dab with a skim coat, and i doubt it got a full bead of adhesive top or bottom. The windows were fitted with straps, and the gaps filled with foam. I siliconed around the inside of the windows, and doors, and stuck the cavity closers on with silicone. Any pipes got a load of silicone around them where they went through the wall. When i got the Air test bloke in i was crapping myself. The first thing he said to me while setting up was that he had just come from a test that had failed with a score of 27. I got a score of 1.8 for 1 house, and 1.7 for the other. I am considering building again in Block and Block. Are there other things that i could do better this time around ?

[joe90]

I built mine like yours and got a similar result and pretty chuffed with the outcome (no letter box or cat flap 🤷‍♂️).

[nod]

Plus 2 

We build block and block land scored similar It’s a myth that solids can’t be airtight I deal with airtightness everyday Mainly commercial But some of our housing sites are taking it far more seriously 

The testing system for the big companies is open to abuse with so many air test companies chasing the same business 

 

 

[PeterW]

19 minutes ago, Big Jimbo said:

Are there other things that i could do better this time around ?

 Make sure the brickies use full perp ends and not a smear and it makes life easier - ask them to point blockwork too. 
 

Wrap the joist ends a la Tony Tray..

 

Airtight tape on windows is expensive but makes a dramatic difference and doesn’t have the issues silicone can have sometimes 

[Pocster]

18 minutes ago, joe90 said:

cat flap

How does your cat get out ?

[Big Jimbo]

I did use about 100 tubes of silicone, but it was only about a quid a tube.

[Pocster]

3 minutes ago, Big Jimbo said:

I did use about 100 tubes of silicone, but it was only about a quid a tube.

10 tubes of lube 🙄🙄🙄🙄

[joe90]

15 minutes ago, pocster said:

How does your cat get out ?

No cat, and a dog I let out when required. 

[joe90]

52 minutes ago, pocster said:

10 tubes of lube

Well his name is “big Jimbo” 😉

[saveasteading]

1 hour ago, Big Jimbo said:

got a score of 1.8 

What everybody else says.(some of it anyway)

Then do your own test ( as ProDave and others).

Tape over all fan and other ducts.

Close or tape over window vents.

 

Dont assume any builder understands airtightness.

 

Then tell the testeron site that  you need 0.8 ( or whatever) and are confident of achieving it.

 

Difficult gaps to complete are at the eaves ( and there is a lot of it) and openings. Examine the detail, discuss with the builder. Supervise.

 

 

 

 

[CalvinHobbes]

1 hour ago, joe90 said:

No cat, and a dog I let out when required. 

My husband calls himself a dog butler.

[Iceverge]

Block house here. 0.31ACH.

 

 

Airtight paint to wall floor junction. 

Airtight paint to all chases. 

OSB window boxes taped to windows and airtight painted to walls. 

Wet plaster to all walls. 

Airtight membrane below cold attic continuously ran over all internal walls. Returned to wall and sealed with airtight sealant. Service cavity for ceiling. Airtight attic hatch. 

 

Our Tony Tray ripped under the hollowcore plank so I cut it away and sealed later with foam and airtight paint. 

 

DIY blower door was the secret though. It really showed up any faults. 

 

 

 

Things I would change. 

 

Pour the ground floor slab over the internal foundation walls continuously and continue the walls from slab again rather than introducing lots of separate areas for leakage.

 

Use the green building store detail for plywood window boxes rather than  fitting OSB ones post window install.

 

Ust the green building store detail for a timber ledgerplate for the first floor. 

 

Pretape the windows before install. 

 

Tape wasn't that dear. About €15 per  25m. Much tidier than foam or sealant. 

 

 

 

 

 

Edited May 4, 2023 by Iceverge

[ToughButterCup]

12 hours ago, PeterW said:

 Make sure the brickies use full perp ends and not a smear ...

 

What's a Perp End please? 

[Iceverge]

The vertical joint in brickwork/blockwork.

[ToughButterCup]

Now show me a smear, please.......

(in other words how does a non-brickie tell the difference betwen the two [a perp or a smear])

[saveasteading]

A fully mortared face between the perpendicular faces of adjoining bricks.

 

For an amateur like me it is tricky. For some "bricklayers" also perhaps.

And many will simply apply the minimum to the front edge for their ease, as they will usually get away with it.

[ToughButterCup]

15 minutes ago, saveasteading said:

.....   as they will usually get away with it.

 

Which is exactly why I asked the question. 

 

For  a 'Switched - On ' Buildhub Member, visiting their build once a day or so, how would she / he tell that the ends were smears instead of full 'perp' ends? 

 

I've spent a little while trying to find examples on YT. No luck.

[Canski]

You can easily tell if the joints are full from the rear of the faced brickwork if it has been built prior to the blockwork. ( only possible with full fill or blown in insulation) 

 

This is (usually) the brickies preferred method. We go round the back and smear all joints full while the mortar is still wet. On some sites now they are asking for the rear of the wall to be tooled with a bucket handle. I think that is a bit over the top.

[saveasteading]

16 minutes ago, Canski said:

I think that is a bit over the top.

 

Unnecessary with a good and thorough brickie. But it does ensure that excess is not poking into the cavity, and that it is compressed.

 

I think I might even pay a little extra for that.

 

Flush should suffice though.

How to check? Brickwork before inner block, makes it visible. 

Alternatively stick a hand down the cavity and feel between the bricks.

 

Some 'brickies' have been doing it for days (they were labourers last week) , and aren't keen on questions. Diplomacy.

Others are stunningly skilled. As with many trades the best ones don't seem to be working as hard but somehow do more in the time. Again diplomacy...they would do it properly anyway.

 

[SteamyTea]

Back to the problem.

Why not just fit a VCL on the inside of the inner leaf? (leaf is such a stupid term for a wall).

 

That way, vapour is stopped before it gets to anything.

Then all there is to worry about is wind driven rain, gutter/roof/cavity leaks and general poor workmanship.

[Iceverge]

Why not just wet plaster it. 

Solves a multitude of issues. 

 

 

[Canski]

@nod what is the approximate S & F price difference between wet plaster and dabbed plasterboard ?

[Big Jimbo]

2 hours ago, Canski said:

@nod what is the approximate S & F price difference between wet plaster and dabbed plasterboard ?

Quite a lot i would imagine....

[dpmiller]

ah but is the PB skimmed or tape&fill?

[Gus Potter]

Lots of good information here.

 

Agree no reason not to adopt masonry constrcution with beam and block floors.

 

It's that attention to detail, good workmanship.

 

A good thing to do is to try and build up you air tightness in layers.. by that I mean don't rely on the final air layer as the last line of defense. All buildings shrink and move as they dry out, settle in so if you can get the underlying layers of construction reasonably air tight they can serve you well as they at least provide some resistance to passage of air.

 

Bit of lateral thinking here. If you have an oriface (a hole / gap) then you can sqeeze quite a lot of air / water gas through that. But if you have a series of orifices they offer much more resistance.

 

For me it's about also trying to get the building staying airtight for say 50 years (it's design life). In  some ways you get less movement with masonry / beam and block construction compared with a TF that moves about a bit more.