Tying into EWI

[Peetz]

Looking for some advice on best way to tie brickwork into existing EWI.

I have a bungalow with EWI and looking to build a small extension to the rear of the property.

I had two ideas, first one was to cut small section of render out and attach 100mm timber to tie in both brickwork and for wallplate but I am a bit wary of doing this as the EWI has a 25 year warranty that I don't want to mess with.

I did contact the company that completed the EWI works to see if they were able to undertake pre and post build works but nothing from them as yet.

My other idea was to use the heavy duty thermax chemical anchors and attach timber or metal plate this way and avoid digging into the EWI, leaving it intact.

Anyone had similar experience or able to advise best way forward??

 

[Deluks]

A proper extension that becomes part of the house?

 

[Peetz]

A proper extension that becomes part of the house?

Yes

 

[Deluks]

Then surely the ewi on the inside will become redundant, you might even be able to remove it and re-use the insulation as part of your build.

Will the extension also have ewi?
You could design the wall as such, and get the original company back to do the ewi, then it becomes their responsibility to join it up to their previous effort. Just check they can do that whilst keeping your original warranty intact.

 

[Peetz]

No the extension will be single skin block with stud partitions, insulation and plasterboard on inside.....rendered to match the existing ewi render.

Yes your right the EWI on the inside will become redundant and I also thought about removing the whole thing on the inside...which would be maximising area within the extension but this would definitely invalidate the warranty on it.

Is using the thermax fixings to attach a plate (existing insulation is 140mm..thermax fixings go all the way to 170mm).... timber or metal and then tying brickwork, roof joists into this a feasible idea or really not fit for purpose??

 

[^woody^]

You don't want to create a thermal bridge by cutting into EWI and connecting a new cold wall to the existing internal wall.

You also need to detail this properly to allow for movement and no water or air penetration.

Has this been designed with plans or are you making it up as you go? It needs thought.

 

[Peetz]

Hey woody, aye...the query of what way to do this has delayed me proceeding with it...I am clear on every other aspect of the build its just the joining of the new brickwork and wall plate to the existing EWI covered wall that's causing me issue.

The Fischer thermax chemical anchors certainly avoid the thermal bridging you talk about but as you say the issue then becomes the space between the attached plate or timber and the EWI.

If I remove a small section of EWI and attach timber directly to the old brick slightly recessed into the EWI and then use timber to masonry ties for the brick work I can then get the whole lot rendered by someone who specialises in EWI...making it waterproof etc. ?? (could use an EPDM membrane between the timber and new masonry??)

(when the EWI company were here this is the process they would use albeit ..timber on first then stuff added around it...but it wasn't complicated....where taps and external fitments go are blocks of recessed timber attached to original brick and rendered over the top..sealed with silicone around fixtures)