100mm block cavity - insulated 60mm aeroboard & 40 mm cellulose fibre

funnyname

hydrus21 wrote: »

Those profiles will create a straight joint which will be subject to cracking if there is any movement.
If the op uses them, I would suggest fixing expanded metal over the joint to reduce the chance of cracking.

What kinda movement are you thinking of and how would you fix the expanded metal?

sydthebeat

hydrus21 wrote: »

Those profiles will create a straight joint which will be subject to cracking if there is any movement.
If the op uses them, I would suggest fixing expanded metal over the joint to reduce the chance of cracking.

You have to expect differential movement whenever you build an extension.

The starter rails are the correct method, but you need to incorporate movement joints at that point. The rails prevent the movement pulling away from the original, but yet vertical movement as the structure settles

funnyname

sydthebeat wrote: »

You have to expect differential movement whenever you build an extension.

The starter rails are the correct method, but you need to incorporate movement joints at that point. The rails prevent the movement pulling away from the original, but yet vertical movement as the structure settles

I've no background in this and am just trying to figure out as much as possible for my own curiosity and to be able to converse with the builder about the works that need doing.

So I'm a half if not a full block short on the inner leaf compared to the outer leaf of the house at the windows. When I take out the old windows, I need to build up either side of the inner leaf so that it matches the outer leaf. Then I'm in a position to get my new windows measured.

Wrt to the vertical movement joints are you talking about this remediated course of one block width (6 to 8 blocks high) having an issue because there's no wall ties in place linking it to the outer leaf?

Also how is it best tied in with the lentil above it?

hydrus21

"The rails prevent the movement pulling away from the original, but yet vertical movement as the structure settles."

There is no way these profiles would prevent pulling away movement from a new extension.
They were designed so that if movement occured between original and new work, building surveyors could determine whether it was
the new or the existing that was moving.
Their main advantage is to be able to join metric brick bond to imperial bond without toothing in.

sydthebeat

When used with movement joints, they do prevent pulling away movements. I've used them on extensions for over 20 years.
Essentially the two structures are designed to be constructed to be independent of each other.
Most cracking and opening joints occur where builders try to tie an existing structure to a new structure with no thought to differential settlement

hydrus21

What kinda movement are you thinking of and how would you fix the expanded metal?
__________________

Were talking hairline cracks from closing windows/slamming doors.
Metal lath is fixed with plugs and screws prior to rendering.

hydrus21

Essentially the two structures are designed to be constructed to be independent of each other.
Most cracking and opening joints occur where builders try to tie an existing structure to a new structure with no thought to differential settlement.

Correct.
40yrs ago, builders were bonding- in new work to old.
When there was subsidence/movement it difficult to determine what was moving.
In the cases i came across it was mainly the existing structure that was the problem.
Profiles were a result of numerous legal cases where homeowners were taking their local authority to court over movement/cracks issues.

funnyname

hydrus21 wrote: »

What kinda movement are you thinking of and how would you fix the expanded metal?
__________________

Were talking hairline cracks from closing windows/slamming doors.
Metal lath is fixed with plugs and screws prior to rendering.

So you tie in the new block to the inner leaf with the yokes (hope that term isn't too technical) from screwfix and then fix the the metal lath at the open cavity side that window will be fixed to? So basically the lath and the profile are the bread of the sambo with the new block the meat?

upupup

funnyname wrote: »

So after a bit more investigation and consulting we've come up with a plan.

First a bit more info tho.

The windows cavities present an additional problem as the inner cavity is tapered away (probably a half block less) from the outer to give curved effect on the revels so more light comes into the room.

The windows need replacing anyways so plan is to get new ones and remediate the inner cavity so that it is flush with the outer cavity and make the placement of the new windows as normal across the cavity. Basic example of what the current window situation looks like within the limits of keyboard characters available

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The trickiest part of the job seems to be the block work to remediate the half block missing from the inner leaf.

Any suggestions on what the easiest method for this is?

Is the position of the new window going to change?ie moving back from the outside leaf.The windowsill position determines where the window sits.

funnyname

upupup wrote: »

Is the position of the new window going to change?ie moving back from the outside leaf.The windowsill position determines where the window sits.

Yeah, plan is to move the window closer to the inner leaf so yeah the position of the window sill is going to change, in fact going to to have to get new ones. Not sure if those will be traditional concrete ones or passive sills. Any suggestions there gratefully accepted as well.

funnyname

So windows have been loosened up and going to move in the existing sills as they are deep enough, hope to get windows measure next week with installation 4 weeks afterwards.

half of the insulation in the southern and western walls has been removed, want to get the rest of it done over the weekend, the pumped cellulose fibre is a pain in the hole to remove as it clogs up the filter in the vacuum cleaner, easy to take out in the more exposed area as the moisture that got in has it harden and clumped whereas in the dryer areas it's very fluffy and breaks up on touch.

funnyname

We're also going to spray foam insulate upstairs as the bedrooms don't hold the heat at all, existing rockwool has fallen out of shape and not keeping heat in or draughts out. There's only a tiny attic so going to take down the sloped slabs above the knee wall and the flat slabs on the ceiling and spray with open cell foam insulation so plan is this is create an airtight envelope from wall plate to the apex of the roof with a 50mm ventilation card between the felt and foam insulation so the roof can breath.

Question, no overall builder looking after this, just ourselves and the engineer with trades (unskilled and skilled) got as required, so just wondering what I can do with the old rockwool and slabs that are going to be coming out of the house, can they be recycled or do I just hire a skip and send them to the dump?

MicktheMan

Caveat emptor:

sprayfoam on its own will likely NOT airtighten your ceiling / roof.

funnyname

https://www.boards.ie/discussion/comment/117778822#Comment_117778822

We will be reslabbing the rooms again, is this not enough or should we also look at putting an airtightness membrane on after the spray foam so it's between the spray foam and slab?

funnyname

More questions of the top of my head

Would it be better to also remove the slab on the knee wall to make it a better/easier job when reslabbing?

When reslabbing should we go for an insulated slab or ordinary half inch one?

funnyname

So all the aeroboard and useless cellulose fiber has been taken out of the south facing cavity, most of the west facing cavity has been done.

I'm caught in the upper lower corners of the gable as there's only one centre window and I can't reach it as well as the other parts.

There's about 2x3 sheets left in place on both sides but with the wall ties and mortar it's fair stuck.

If the inner gable leaf was taken away I'd get it no bother but I don't want to go to that extreme.

Anyone have any ideas? Could I just leave that in-situ and pump the rest of the cavity and hope for the best?

funnyname

Photos to help

funnyname

View from below of top left and right corners.

10-10-20

Was it determined whether the dampness was interstitial condensation or the permeability of the external wall? If the latter, will this be remedied?

funnyname

It was interstitial condensation