Digmixfill

Creating new cavity and wonky walls?

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I've got to build inner leaf to create a 100mm cavity against existing 225mm brick outer walls. The existing walls are anything but straight which means that if i built the inner leaf true the cavity will change size quite a bit on some walls.  The roof wall plates will be on the new leaf when it is replaced.

 

My question is should i build the inner leaf straight and try to average out the cavity space or should i construct the new leaf to follow the undulations of the existing walls to maintain a 100mm cavity?

 

 

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How are you dealing with the foundation for the new wall?  How far out of true is the existing?  Did you look at doing the inner leaf in timber frame, as you only need a residual 50mm cavity and you can insulate in the depth of the frame.

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How are you going to tie both skins together??

What kind of insulation is going in between??

Any particular reason for using block as @ProDave said on your other post why not do it in timber.

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If you keep a true cavity then you will have a wonky inner wall

is that what you want, wonky walls might look good in a 200 year old cottage, but I would much prefer mine nice and true. 

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@ProDaves and @Declan52s suggestion of using an inner structural timber frame gets my vote.  You can include insulation within the timber frame, resolve all the issues with things being out of true and still preserve the external appearance.  What's more, even if you used low decrement delay foam insulation internally, to minimise the loss of room space, the overall decrement delay factor would still be high due to the high heat capacity outer skin.

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Thanks for the replies :)

 

It's an old brick barn and the alterations it has had, roof failing and general movement over time have taken its toll.

 

I've underpinned the entire building and extended the concrete inside to serve the new inner leaf. (My username is based on this joyful task)

The leafs will be tied together with wall ties resin bonded into the existing brickwork.

Insulation will be full fill.

 

The worst measurement i have shows that one wall is > 100mm out of true at one end due to the wall bowing and twisting at the same time. Most are +/- 50mm at some point along them.

 

If I changed to timber frame now I'd have to submit changes to the plans and whatnot.  It's an option i suppose but i'd prefer the new inner leaf.

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11 minutes ago, Digmixfill said:

The leafs will be tied together with wall ties resin bonded into the existing brickwork.

Insulation will be full fill.

 

So pick the min 100mm and work from it. Some gaps will be bigger than 100mm but none will be smaller. Then get blown bead insulation installed - fills every cavity and you will have no gaps and a really decent level of insulation. 

 

The only plans you would need to change for TF would be for BRegs as planning doesn’t care what the inside looks like ...

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Fair point on the plans. It was building regs that i had in mind when i mentioned plan changes.

 

The insulation choice at the moment is glass wool batts. The datasheet for these suggests that a +/- 15mm irregularity is fine but i'll need to get creative on the larger spacings.

 

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Glass batts are fine for regular cavities but this will end up a right mess - seriously consider blown bead as it’s quick and efficient and would be ideal for this sort of job. 

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Surely this should be led by asthetics? If you make it die straight inside and it’s wonky outside will it feel right? My natural reaction would be to embrace the wonkage. 

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You'll live in the inside of the house and be looking at the internal walls all the time. Do you want to look at straight or crooked walls? If it was mine they would have to be straight and flat, but that's just me.

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I agree with @PeterW Consider blown bead insulation. Glass wool batts will be a disaster with a cavity that varies as much as yours.

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As the internal walls are structural you will need to keep them as straight as possible otherwise you will get issues with wall plates and loading and may need to go thicker blocks just to get strong enough wall. Plastering will be a nightmare too..!!

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On 04/07/2018 at 07:15, PeterW said:

Glass batts are fine for regular cavities but this will end up a right mess - seriously consider blown bead as it’s quick and efficient and would be ideal for this sort of job. 

 

Is the blown bead DIYable? I've had a quick look around but i've only come across "professional" install.

 

On 04/07/2018 at 08:47, PeterStarck said:

You'll live in the inside of the house and be looking at the internal walls all the time. Do you want to look at straight or crooked walls? If it was mine they would have to be straight and flat, but that's just me.

 

I had the notion that EVERYTHING would be perfect and square before I started. The century old building has seen that idea off.

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4 hours ago, Digmixfill said:

 

Is the blown bead DIYable? I've had a quick look around but i've only come across "professional" install.

 

 

I had the notion that EVERYTHING would be perfect and square before I started. The century old building has seen that idea off.

 

The ONLY things that are perfect and square are probably squares. :ph34r:

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5 hours ago, Digmixfill said:

 

Is the blown bead DIYable? I've had a quick look around but i've only come across "professional" install.

 

 

I had the notion that EVERYTHING would be perfect and square before I started. The century old building has seen that idea off.

 

You can’t DIY blown bead but the cost is so low compared to other methods it’s just not worth trying to even work out where to start..!

 

Quotes for graphite bead were around £1600 installed for 150 square meters at 150mm cavity. Think that’s £70/cuM and comes with a 25 year guarantee. 

 

It was installed in 2 hours ..!

 

Cavity Batts came in at around £60/cuM for the same thickness but there is then Labour abd installation on top. 

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Has an engineer looked at the building?  It is important that the external brick wall is properly stable and restrained, otherwise it may compromise the structure.  If you want to go blockwork internal, it must be built plumb.  You will need a selection of wall tie lengths.  Do as @PeterW suggested with blown in beads.

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19 hours ago, Ferdinand said:

 

The ONLY things that are perfect and square are probably squares. :ph34r:

No argument from me there.

 

18 hours ago, PeterW said:

 

You can’t DIY blown bead but the cost is so low compared to other methods it’s just not worth trying to even work out where to start..!

 

Quotes for graphite bead were around £1600 installed for 150 square meters at 150mm cavity. Think that’s £70/cuM and comes with a 25 year guarantee. 

 

It was installed in 2 hours ..!

 

Cavity Batts came in at around £60/cuM for the same thickness but there is then Labour abd installation on top. 

 

I've found beads that have a marginally better U value than the batts i'd decided on, so that's a plus.

I'm trying to do everything myself, so labour costs tend not to factor in.  Batts are currently  going to cost me 7.55/m2 for 100mm roughly £81/m3.

 

 

13 hours ago, Mr Punter said:

Has an engineer looked at the building?  It is important that the external brick wall is properly stable and restrained, otherwise it may compromise the structure.  If you want to go blockwork internal, it must be built plumb.  You will need a selection of wall tie lengths.  Do as @PeterW suggested with blown in beads.

 

We had a structural engineer take a look at everything before we started. The only works required was underpinning.

 

Whilst doing things today i noticed one corner where the wonk was obvious to the naked eye. Pictures attached.

 

 

lower_part.s.thumb.jpg.018bb7e6ed027da30a8984284ea26bc5.jpg

 

upper_part.s.thumb.jpg.6f5f240a79c7886c9c4b9d46b3d3446f.jpg

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4 hours ago, Digmixfill said:
23 hours ago, Ferdinand said:

 

The ONLY things that are perfect and square are probably squares. :ph34r:

No argument from me there.

According to my wife the only things that are perfect are women! I can’t argue with that! 

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Posted (edited)
9 hours ago, Triassic said:

According to my wife the only things that are perfect are women! I can’t argue with that! 

Is that because she is right of because she is your wife?

?

Edited by Ferdinand

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15 hours ago, PeterW said:

@Digmixfill where in the UK are you based...?

 

Staffordshire.

 

I have this thread set to notify me of replies and my settings say immediate notification but I'm not seeing any email notifications. (No obvious delivery failures in my email server log either). Are newbies excluded from notifications?

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