Is a single block inherently air leaky?

[epsilonGreedy]

The prevailing view in this forum is that air leakage is a larger problem with brick & block construction and that a wet plaster lining is a good solution for reducing air leaks.

 

I am not clear where exactly air leakage occurs with brick & block construction. Is a single block air permeable right through the core of the block or does warm air wriggle out of a house structure at the periphery of window and door apertures through the course granular concrete casting of the outer 1cm of a block's surface?

[Nickfromwales]

@tonyshouse blog will serve you well with the old heavy / wet build approach. 

If im ever lucky enough to build, there won't be a brick or block in sight. A decorative stone facade maybe, but no block internal layer that for sure. 

[Russell griffiths]

If you where to build a single skin block garage (As an example) stand outside with a hose spraying on the wall and see how quick the water penetrates to the inside, couple of minutes if your lucky, I presume this would demonstrate how porous a concrete block actually is. 

[joe90]

Is this not why blocks should be rendered ( like my garage) to prevent weather ingress. Yes I am a fan of Tony,s build and that is one of the reasons I have gone block and brick with full wet plaster airtight inner.

[epsilonGreedy]

20 minutes ago, Russell griffiths said:

If you where to build a single skin block garage (As an example) stand outside with a hose spraying on the wall and see how quick the water penetrates to the inside, couple of minutes if your lucky, I presume this would demonstrate how porous a concrete block actually is. 

 

 

Ok I am convinced, only slightly better than building a wall out of structural milk bottle crates.

 

I can feel another question brewing about sealing an inner block wall.

[epsilonGreedy]

10 minutes ago, joe90 said:

Is this not why blocks should be rendered ( like my garage) to prevent weather ingress. Yes I am a fan of Tony,s build and that is one of the reasons I have gone block and brick with full wet plaster airtight inner.

 

I am beginning to see the wisdom of this, no point chasing u values in the loft with an extra 100mm of loft insulation roll without addressing air exchange. As @ProDavesays, expecting dot and dab dry lined plaster board to provide a sealed inner tent does not work due to all the cut outs. And as @JSHarrisobserved, dot and dab dry lined plaster board creates a nice vertical air convection void against the inner block wall.

[PeterW]

The new foams rather than dot and dab certainly get round that issue as there is 1-2mm at most between wall and board. Walls also feel a lot more solid. 

[epsilonGreedy]

20 minutes ago, PeterW said:

The new foams rather than dot and dab certainly get round that issue as there is 1-2mm at most between wall and board. Walls also feel a lot more solid. 

 

 

This indeed popped onto my radar of possibilities but then dropped off when I imagined my diy attempts of fixing using low expansion foam. If this stuff is time sensitive I fear adjacent plasterboard panels will be recessed or proud by a few mm as the stuff cures during my pounderous diy fixing. The YouTube videos are convincing.

 

Another diy attraction of the extra 25mm insulation layer is that it will be more accommodating of my first & second fix pipe & cable routing, I assume?

[PeterW]

You can’t bury wires in insulation unless you rate them correctly. 

 

The purpose made foams are pretty Impressive - we got decent levels all round even on some old walls that were far from plumb ..! Once it’s skimmed you never see it anyway ... find a good plasterer ..!

 

[epsilonGreedy]

2 hours ago, PeterW said:

You can’t bury wires in insulation unless you rate them correctly. 

 

 

I should have anticipated the over heating issue. Reading further on this topic since your post I understand lighting circuits are not much of an issue particularly given the short buried cable run. Kitchen cooker circuits = potential ouch. Which leaves the normal socket rings, will have to do some careful calcs... possibly run these cables up against the wall in lightly chased ducts with metal protection conduit facing over. Got 6 months to research this now that the other thread on parge coat block sealing options has scoped sealing the inner block wall down to a <4 day task.

[joe90]

When chasing cables into blockwork only plastic capping is used under plaster so why not the same under foam/plasterboard/skim?

[Nickfromwales]

21 hours ago, joe90 said:

When chasing cables into blockwork only plastic capping is used under plaster so why not the same under foam/plasterboard/skim?

Gypsum and cement soak into twin and earth cable and rot the copper inside. Drilling a hole through dry is not a problem, its when its applied wet that the issue occurs. Twin and earth cable is quite fragile, whereas some folk think its bulletproof. Pull two pieces aggressively against each other for a metre or so and see what happened to the static piece. Like a knife through hot butter, straight down to the copper. 

The plastic capping is only top stop wet products getting to the cable, nowt else ( as it won't show up on a detector for eg ). Metal cappings won't stop a drill bit or nail either so take lots of pictures before boarding. 

For kitchens run the cables horizontally so you dont have to worry when fixing the wall cabinets. 

I dont see the reward from all the effort of block internal vs TF TBH. DIY maybe an argument but after that im a bit confused.

TF for me, as which other system can take you from foundation to weathertight 2-storey build in 7-8 days, or less? Less worry about trades and detailing then too as the airtightness of a TF is achieved by the membrane rather than bucketloads of wet parge and lots of fiddly pointing / troweling. 

Pay the extra and get your pozi-joists at tighter centres, and go for blown cellulose, and then its nice and "solid" feeling and super quiet too. 

[PeterW]

There is a good argument for making all internal walls (where possible) TF and then only inserting sockets and pipework into these walls. 

 

It is quicker for the follow on trades; there is no chasing out of walls; there are no caps or other protective measures needed (subject to wiring regs..!!)

 

It takes planning but it can pay real dividends - your other option is create a service void by using battens and then at least insulate the “spare” gaps that have no wiring or pipework.