External Insulation DIY - questions

I am looking to do a DIY External Wall insulation project, but have a couple of questions. The house has solid walls on three sides, the rear has a new ground floor extension.
The rear of the house backs to an open field so gets brunt of wind.
The side of the house is to an alley way, so not closed area, again gets a fair amount of wind.
The front of the house is facing the street, so again is open to the elements. The back and side are flat, but the front has two round bays (the bottom one is brick to window, then timber frame to the first floor window, and then timber frame to the loft). The ground floor gap has been filled with PIR and foam filled. The first floor bay as yet to be done. Both bay's are tiled on front.

The questions i have are:


1) Two layers of 50mm each staggered any different to 100mm single layer if both are properly joined and butted against each other?

2) As I’m looking to install myself, I will be taking guttering and boards off under the roof, and putting the boards above the facia height, before putting the guttering back. Any issues with this?

3) What is the best way to refix soil pipes/sky dish etc once the boards are on and rendered? Someone suggested putting wooden blocks in place of the PIR and screw into that. To me, that introduces cold/hot spots but may be the norm?

4) There are some existing holes from old tumble dryer etc. What is the best way to fill these? Brick cut to shape, block cut to shape, fill with foam, board over, something else?

5) Windows, I’m looking to replace the windows at the same time, so what is the best way to fix the new windows, some suggest an 18mm ply box created inside the existing opening which allows the windows to come out, giving the appearance that they are still “Standard” distance from the wall when really the are now fixed to theouter PIR rather than brick. Inside window cill will be bigger, but I’m happy with that. Is this a good way to do so? (I would set back the ply enough so that it isn’t touching the outside layer) or is there an alternative?

6) Fix window first or boards?

7) I have pebble dashing on the existing wall, but the pebbles are coming off, best to take the pebble dashing off back to brick and attach the PIR to the wall? Or leave render on?

8) Lastly, any problems with leaving the boards un rendered till the summer if I do the insulation now? Or is it better to render asap? ( looking to do the back wall now as its only half height due to extension, then spring the side as all my pipe work is there, which needs to be moved, repiped from the ground up) Then the front hopefully later in 2018 as I want to redo the porch at the same time. Should I get it rendered as I go, or wait till all done and get it rendered in one hit?

And any recommendations as to what products to use for the insulation?

I didn't DIY mine but did a lot of research at the time and watched mine being done so have some knowledge.

3) I've seen the wooden block method mentioned a few times but everything on my house was re-fixed to the wall with long bolts through the insulation. Nothing has moved since installation.

4) Anything really. It's not structural and will be covered and made watertight by the render. I filled a few pipe holes with expanding foam and the people doing the EWI said it was fine.

5) We had our windows put in after the insulation. The window company recommended doing it this way because it was easier for them to work out the correct depth for the cills. The job would have been neater if the insulation was done after because some had to be cut to get the old ones out. They fixed the windows as close to the edge of the original walls as possible so I have deep reveals. I suspect a ply box would have been a lot of effort for very marginal gain and I've not really noticed any issues with the window placement.

7) Our render was in a terrible state and was left on. Boards are fixed through to the bricks. As long as the wall is level you don't need to take it all back (it's also very messy and disruptive).

8) I think insulation reacts with sunlight so ideally you shouldn't leave it uncovered. The council sent round a surveyor after ours was finished who checked for this as part of his report. The flip side is that your render won't match if you don't get it done all at once.

If you insulate the wall in the alley you'll be projecting into that space - do you have permission to do this from the owner? I'd also be nervous about people knocking and damaging the insulation, once rendered it seems fairly robust but suspect it could be damaged fairly easily (we were told to make sure anyone using ladders had rubber protectors over the end etc).

m0t said:

If you insulate the wall in the alley you'll be projecting into that space - do you have permission to do this from the owner? I'd also be nervous about people knocking and damaging the insulation, once rendered it seems fairly robust but suspect it could be damaged fairly easily (we were told to make sure anyone using ladders had rubber protectors over the end etc).

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Thanks for the responses, In terms of windows, this is the bit that is confusing, some people say do windows first, some say after. I'm now thinking do them both at the same time - so put boards on the wall, fix window, render boards!

Re above - there is a walkway which is mine - approx 1m wide, then the community alley way, so any works etc will be carried out on my land, but for wind/rain it is open to the elements! (Should have made this clearer).

What insulation are you using?
You should fix your windows first as it's much easier, you can either use a ply box; timber batters on the wall or window brackets.
If you use a 180mm cill is a standard size so you can stick about 50mm on your brickwork and then this gives you 20mm drip and then you can fix normally. The ideal solution is to have the window inside the insulation so just forward of your brickwork though.

You should try and get it covered asap not only to protect it from mechanical damage but you might get water behind the boards etc.

tomfe, open to suggestions at this stage,
window inside the insulation is possible - if the window can fix within 100mm, and the window can fix securely to the insulation board, or i can engineer something to sit in the insulation for the window to attach to!

I've seen a couple of designs on https://retrofit.support/
they use woodfibre insulation, two layers by the looks of it, and the window frame sits inside the first layer. A ply/softwood box goes in the old window hole to cover the existing brickwork.

specifically looking at this setup:
https://retrofit.support/detail/75/

I would use EPS over PIR, as it's less likely to degrade when wet. I know it's not as good thermally but there are know issues with phenolic and it falling off walls.

No doubt you've seen this image however it would be better done in cement board, this is a way another is just to add timber batons around the windows to fix into, there is a bit of fiddling cutting (a rabbit in the back) the boards accommodate the timber.


Similar to this, however your batons need only be 50-75mm deep, I'd also fix the windows normally with either brackets or fixing through the frame into the timber.

For large tall windows and bifold I use steel angle just for the bottoms.

Or for max efficiency there are a couple of high density foams on the market which will take fixings, compacfoam.

Tomfe, that's basically what I was thinking in terms of fixing the windows. (Though not sure how I can do the round bay and keep it strong!)

Do you have pics of the internal setup of those? Or drawing of the cross section?

Re render and your point 8 above, I had an Alumasc system with Kingspan K5 phenolic boards fitted about 3 years ago. In that system there were 3 coats of 'render' applied:

• First coat was an adhesive that bedded a fibre mesh over all the boards
• Second coat was a fibre-reinforced base coat. This was just grey, but the installers told me it was weatherproof after that had been applied. This coat provides most of the strength to the render
• Final coat was a coloured silicon top coat

Therefore, if you have a similar system, you could do all of the rendering except the top coat. Then your system would be weatherproof and you could apply the top coat at a later date to get an even finish all over.

unclebob1 said:

Do you have pics of the internal setup of those? Or drawing of the cross section?

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No but there's nothing complicated about it, it's just a box. You can make it full reveal depth or not just think about how you are finishing the internals.

nebjamin said:

Then your system would be weatherproof

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The base coat is not weatherproof but if you paint it with the primer it will be for a bit.

tomfe said:

The base coat is not weatherproof but if you paint it with the primer it will be for a bit.

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It is weathertight according to the manufacturer's data sheet: http://www.alumascfacades.com/media/163179/pd109fa-m.r._scrim_adhesive.pdf

nebjamin said:

It is weathertight according to the manufacturer's data sheet: http://www.alumascfacades.com/media/163179/pd109fa-m.r._scrim_adhesive.pdf

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I would note the words weathertight as you say. Why do you think they use that wording? Also I don't know if it's still the case but Almasc is rebagged so you used to get inconsistencies across a product.
For the sake of an extra couple of hours you'd be better off sticking the primer ontop to make sure it'll last. I would also not use phenolic, it degrades when wet.

Thanks for the replies, due to amount of work I feet I'll end up giving this out to someone, need to re pipe soil and rain water pipes from chamber to roof, insulate, create window boxes for round bays, and screed. Not happening fast with a 9-5 job on top

Any thoughts on the single layer Vs two layers? The window box design I'm looking at makes me think two layers, first layer butted op to wooden frame, second layer then over installed window?

We had ours done 2 years ago. We replaced the windows first and just pushed them so they were flush with the front of the building - no boxes built.

For things like satellite dish, decking posts, soil stack and outdoor lighting, I fitted pieces of 75mm x 75mm timber in the correct places and left a screw sticking out of the middle to find it again after insulating. (We had 90mm EPS boards used, the timber I fitted was just filled to level using base coat.

Take care if laying cables for outdoor lighting, EPS will eat the insulation!

If I knew what I do now, I would have removed the soffits and pushed the boards to the top - we are now suffering cold spots at the top of the walls. You will also need to find a way to insulate the TOP of the old walls. I am doing that next week with rockwool from inside.

Soil stack and drain pipes were a bit of a faf as the old was one was cast iron, so had to be cut to the ground, then an adapter fitted and then 2x 45degree angles to pull it out the correct distance.

Regarding old holes, just ignore them and board straight across, we did that with badly places air vents.

I can upload some progress photos if you wish?

phatboy said:

We had ours done 2 years ago. We replaced the windows first and just pushed them so they were flush with the front of the building - no boxes built.

For things like satellite dish, decking posts, soil stack and outdoor lighting, I fitted pieces of 75mm x 75mm timber in the correct places and left a screw sticking out of the middle to find it again after insulating. (We had 90mm EPS boards used, the timber I fitted was just filled to level using base coat.

Take care if laying cables for outdoor lighting, EPS will eat the insulation!

If I knew what I do now, I would have removed the soffits and pushed the boards to the top - we are now suffering cold spots at the top of the walls. You will also need to find a way to insulate the TOP of the old walls. I am doing that next week with rockwool from inside.

Soil stack and drain pipes were a bit of a faf as the old was one was cast iron, so had to be cut to the ground, then an adapter fitted and then 2x 45degree angles to pull it out the correct distance.

Regarding old holes, just ignore them and board straight across, we did that with badly places air vents.

I can upload some progress photos if you wish?

Click to expand...

Soil stack, got cast iron too, and it's in the wrong place, so I'm thinking of replacing all the way from man hole (the new location is only a meter or two from where manhole is do easier to start fresh then mess about with the existing.

I'm aiming to take the Sofit boards off and push the insulation up as much as possible, then trim and refit the boards.

With regards to wires, noted, will run on the outside or in poly pipes!


Any pics are appreciated!