Extra length cavity wall ties for wide walls

[Fallingditch]

I have completed the ground floor inner leaf of my three storey, fairly secluded house. So as to get Planning approval, it is designed to look like an East Anglian tide mill. It will be clad in white fibre cement weatherboard, with the third storey living space in a gambrel (Dutch Barn) slate roof. 

It’s in flood zone 3a. It’s designed to be flood resilient (even though there’s no evidence of it flooding, ever) which means that it must be built in a way that if 300mm of seawater washes in, it won’t do too much damage while it’s there.

For that reason, it's primarily being constructed of double skinned blockwork with 200mm EPS in the cavity.

I didn't want to pile so foundations are a reinforced insulated concrete slab designed by TSD (even though we are on London clay).

I did consider a single skin structure, but the requirement to clad the building in weatherboard meant that I concluded that an external block skin was going to be the most practical way of holding the cladding up. 

I am using Ytong aerated concrete blocks on thin bed mortar. I hope this will lead to better airtightness - they are also be easier to handle, shape and and lay. Ytong were the only option above two storey (greater compressive strength.)

Walls will therefore be 215mm inner, 200mm EPS and 100mm outer - total width 515mm.

Construction sequence is: 

• build inner skin
• parge outer face of inner skin (airtightness)
• fasten EPS to outer leaf of inner skin (airtightness)
• build outer skin close up against EPS
• insert (say) 375mm wall ties through outer leaf, EPS and into inner leaf

Long wall ties like this can be very expensive (for example, those from a company called Helifix might be £3.50 each ...). So I am looking for a more cost effective supplier.

I also don't know how many I should be fitting?

Ideas?

(There was a posting In Another Place entitled "Helical Retro Fit Wall Ties" - I guess that's probably still relevant?)

 

 

 

[tonyshouse]

I used basalt fibre ones to mitigate thermal bridging, they were expensive and I built them in as work proceeded.

spiral metal ones can be retrofitted

[DeeJunFan]

There is an Irish company called vartry engineering. They specialise in wide cavity ties. I was quoted about .70 cent for 200mm cavity ties. So about 55p each.

[thomas]

Could you forgo the external leaf and do an effect with render on the outside?
Seems a bit mad to me to just build a wall to have it covered in cladding.
Or 300mm eps and then battens the extra thickness should counteract any thermal bridging from fixings.

[Inchbyinch]

I'm in the same boat but I'm going with 215inner and 100 outer leaf. 

I'm thinking of qwik fix which are about €1.60 ex VAT. 

Www.killeshal.com

any one experience with these?

[tonyshouse]

I can't see any point in having a 215 inner skin as part of a cavity wall, better to have 2 X 100 skins and use the extra space for insulation.

[Fallingditch]

23 minutes ago, tonyshouse said:

I can't see any point in having a 215 inner skin as part of a cavity wall, better to have 2 X 100 skins and use the extra space for insulation.

It's three storey. I used Hilliard Tanner to do the reinforced insulated slab and the overall structure. It came back with 215 inner leaf.

Re the outer leaf. You are right it's only there to hold up the cladding. If I was doing it again I would certainly have applied for planning with a single skin with EPS and render. Who knows they might even have said yes! And it might have been possible to make render look like weatherboarding....

Anyway now Arctic white weatherboarding is now a condition...