EWI with cantilevered external fixtures - eg. sunshades

[Crispy75]

Hi, long time reader first time poster

 

As part of a comprehensive retrofit and extension project I will be insulating my existing brick and new timber frame walls with at least 200mm EWI. I'm comfortable with specs/details for the basic buildup, but would like some advice WRT to through-insulation fixtures, in particular:

 

I want to install brise soleil or awnings to south-facing windows to cut down on summer solar gain.

I also plan to support one edge of a pergola at ground floor (so a long beam fixed to the wall).

 

I can't seem to find a standard method for achieving this. I don't want to simply bolt something direct to the brick with a Farat pad and insulate/render around it. I'd rather provide a secure surface directly behind the render so the awning, beam etc. can be as simply fixed as if it was a solid wall.

 

I've found the SWFix product, but that doesn't seem geared to anything heavy or cantilevered.

 

Has anyone solved the same problem in an elegant and robust way?

I'm not going to just bulk it out in timber am I?

 

[Alan Ambrose]

Interesting question. The only somewhat load bearing but thermally insulating materials I can think of are Marmox and Foamglas. Farrat pads are made of glass reinforced polyester apparently. Another option here maybe:

 

https://www.rhnuttall.co.uk/gaskets/nylatron-thermal-breaks/#:~:text=Commonly termed thermal bridge breakers,to unmodified cast nylon grades.

 

- nylon with some stuff. SS is better thermally than standard steel I’m told.

[MikeGrahamT21]

You’ll likely need to import them, but these will do the job

 

https://www.celofixings.com/heavy-duty-system-resitherm/1473-resitherm.html

[Alan Ambrose]

Don’t know whether it’s just my in-built cynicism, but it seems a bit hard to find out for these products (a) what materials are used and what kind of arrangement and/or (b) what the thermal numbers are.

 

e.g. what’s going on here? Standard bolt into fibre filled nylon? Metal threaded insert in the nylon? Hows that held into the block? Is that such an amazing insulation breakthrough?

 

Edited August 26 by Alan Ambrose

[Alan Ambrose]

For the RH Nuttall stuff: “Thermal conductivity and load bearing data of our high specification Nylatron Thermal Breaks are both readily available on request.”

 

Yeah, right.

[ProDave]

How much does the thermal bridge of the fixing bother you?

 

For my timber frame hose with 100mm wood fibre cladding, I drilled a 1" hole through the wood fibre, stopping when it reached the timber behind it.  nserted a 120mm aluminium tube as a spacer, well sealed as it was inserted with Sikaflex.  Then a very long coach bolt through what I was fixing (balcony) through the spacer and into the wood.

 

In my case it was not really a cantilevered load, the balcony stood on legs, it was just to fix it to the house.  The 120mm spacers meant there was a gap between the balcony frame and the finished wall so it was not compressing the wood fibre.

 

The small amount of thermal bridging using metal fittings never concerned me.

[TommoUK]

Timber will be cheapest but may not give you the look you want. Have a look at horizontally mounted aluminium brise soleil systems. Lower profile than timber, light weight and easy to fix to the structure. Most suppliers will provide recommended fixing details and /or brackets

[saveasteading]

8 minutes ago, ProDave said:

The small amount of thermal bridging using metal fittings never concerned me.

It did me once upon a time. Then I included the fixings in a wall conductivity calculation.  It becomes lost in the decimal places.

The bolt shank is say 10mm dia. The thread doesn't matter. Consider that in proportion to the wall area.

Yes real heat will pass along the fixing, but you can stop a lot  of it with a cap outside.

 

You can work the fraction out yourself, for your own comfort. The convert that to £ and you will relax about it.

 

It is very much more important to have a permanently solid fixing, and supervise it,  if not doing it yourself.

I would include some redundancy in that, eg if the calculations say you need 3 fixings, use 4.

Why? because things go wrong in building...eg there may be a flaw in the wall. 

 

[joe90]

18 minutes ago, ProDave said:

The small amount of thermal bridging using metal fittings never concerned me.

@ProDave beat me to it. A bit like cavity wall ties, the benefit of non steel was not worth it IMO. If the “rawlplug” is thick enough it will insulate the fixing anyway. The area of fixings compared to the wall is minimal.

[Crispy75]

Thanks for the replies!

 

Yeah I'm not too fussed about cold bridges from a few screws or bolts, but doing an offset frame in timber will be a pain to fit the EWI round. Lots of cutting and glueing and scraping and cursing. Thought there might be a "big chunk of GRP or nylon with nice square edges and concealed fixings" kind of solution. My experience in the construction industry has lead me to believe that you have to make things as simple as possible for builders if you want anything approaching a careful job. Much rather spend extra upfront on a clever product than have my carefully annotated NASA-grade details ignored or bodged.