Buying a Refurbished Flat with External Wall Insulation – Any Advice?

alwaysquestioning

I’m in the process of buying a recently refurbished flat that had external wall insulation (EWI) installed last year. I’ve heard that the key to good insulation is using the right materials and ensuring a reputable company did the work properly.
However, I’ve also read some horror stories, which is making me a bit anxious.|

Details About the Property & Insulation

• Year built: 1950 (from my understanding it is all solid brick apart from a recent extension that has cavity wall.)

• Solid brick with external insulation – EPC rating: Good

• Recent extension with cavity walls – EPC rating: Very Good

• LOFT Pitched, 250 mm loft insulation - Good

• EPC score 75

• Insulation material used: K Systems M, 50mm external rockwool dual-density slab https://k.systems/solutions/systems/k-systems-m 

• No warranty provided: The seller (a developer) isn’t offering a warranty on the insulation. From my research, trusted companies usually offer 10-25 years on EWI—so is this a red flag?

Ventilation & Condensation Concerns

The flat has an MVHR system (Blauberg model) installed in the loft. I assume this will help with air circulation, but I’m wondering:

• Is Blauberg a reputable brand for MVHR systems?

• Will this be enough to prevent condensation and mold issues inside the flat?

Survey Results & Potential Issues

I had a survey done, and the surveyor used a thermal camera, which detected cold-bridged areas around a window. He believes this could be caused by overflowing gutters and drainage issues soaking the walls. I’ve asked the seller to fix the gutters, but I’m not sure if that will actually solve the problem—or if there’s an issue with the installation of the insulation itself.

My Concerns & Questions

I know that, in theory, external insulation is beneficial, but I’m worried that poor installation or hidden issues could turn this into a nightmare.

1. Is “K Systems M, 50mm external rockwool dual-density slab” a good material for EWI?
   
   
2. Should I be worried about the lack of a warranty?
   
   
3. Will fixing the gutters solve the cold-bridging issue, or could it indicate poor insulation installation?
   
   
4. What tests or checks can I do to be 100% sure the insulation is properly installed and won’t cause long-term issues?
   
   
5. If EWI is installed incorrectly, how difficult/expensive is it to fix? Could I be stuck with major repair costs down the line?
   
   
6. Would it be worth getting an independent EWI specialist to inspect the insulation? If so, what would they typically look for? any practical, non-invasive inspection methods they can use to check the insulation?
   
   
7.  Which professional should I call to inspect the insulation and ventilation?
   
   
8. And, of course, the evergreen question—if you were in my shoes, what would you do?

I’d really appreciate any advice or experiences you can share!

Thanks!

MikeJXE

I would walk away, too many red flags 

FreeBear

alwaysquestioning said:

• Insulation material used: K Systems M, 50mm external rockwool dual-density slab https://k.systems/solutions/systems/k-systems-m 

• No warranty provided: The seller (a developer) isn’t offering a warranty on the insulation. From my research, trusted companies usually offer 10-25 years on EWI—so is this a red flag?

My Concerns & Questions

I know that, in theory, external insulation is beneficial, but I’m worried that poor installation or hidden issues could turn this into a nightmare.

1. Is “K Systems M, 50mm external rockwool dual-density slab” a good material for EWI?
   
   
2. Should I be worried about the lack of a warranty?
   
   
3. Will fixing the gutters solve the cold-bridging issue, or could it indicate poor insulation installation?
   
   
4. What tests or checks can I do to be 100% sure the insulation is properly installed and won’t cause long-term issues?
   
   
5. If EWI is installed incorrectly, how difficult/expensive is it to fix? Could I be stuck with major repair costs down the line?
   
   
6. Would it be worth getting an independent EWI specialist to inspect the insulation? If so, what would they typically look for? any practical, non-invasive inspection methods they can use to check the insulation?
   
   
7.  Which professional should I call to inspect the insulation and ventilation?
   
   
8. And, of course, the evergreen question—if you were in my shoes, what would you do?

Have a look at the BBA certificate for the K System EWI -> https://s3.eu-west-1.amazonaws.com/k-systems.s3-assets.com/5744ps4i1-K-Systems-M-VBriQ-EWI-System.pdf According to the table on page 10, at least 110mm is required to hit the 0.30 Wm²/K requirement set out by building regulations. 50mm falls well short so I'd be asking for Building Regs completion certificates.

The BBA cert also mentions that appropriate measures are taken to prevent interstitial condensation. Unfortunately, without doing invasive investigations, there is no way to confirm that the work has been done correctly. So to answer your questions -

1. meh. Needs to be a lot thicker.
2. yes.
3. No. But a dry wall is thermally more efficient than a wet one.
4. Ask (no, demand) completion certificates issued by Building Control.
   
5. Repairs could be very costly. Especially if lots of scaffolding is needed.
6. Visual checks won't reveal any hidden issues - Would need to poke holes to see.
   
7. The surveyor that you used to do a building survey (level 3) will be able to advise.
8. Me personally - Buy a freehold house, but each to their own.
   

 

alwaysquestioning

FreeBear said:

Have a look at the BBA certificate for the K System EWI -> https://s3.eu-west-1.amazonaws.com/k-systems.s3-assets.com/5744ps4i1-K-Systems-M-VBriQ-EWI-System.pdf According to the table on page 10, at least 110mm is required to hit the 0.30 Wm²/K requirement set out by building regulations. 50mm falls well short so I'd be asking for Building Regs completion certificates.

The BBA cert also mentions that appropriate measures are taken to prevent interstitial condensation. Unfortunately, without doing invasive investigations, there is no way to confirm that the work has been done correctly. So to answer your questions - 

thanks for your reply, really really useful, I didn't check that table.

This is all new to me, so I'm still learning how everything works.

can I ask you what are the implications if insulation doesn't meet the requirements set by building regulations?

I assume there could be issues when selling the property, or insurance, but are there any other potential problems I should be aware of?

Apart from the certificates issued by Building Control, are there any other documents the seller can provide to protect me in the future? I want to make sure everything is in order and avoid any potential issues down the line.

FreeBear

alwaysquestioning said: can I ask you what are the implications if insulation doesn't meet the requirements set by building regulations?

I assume there could be issues when selling the property, or insurance, but are there any other potential problems I should be aware of?

Apart from the certificates issued by Building Control, are there any other documents the seller can provide to protect me in the future? I want to make sure everything is in order and avoid any potential issues down the line.

With reduced levels of wall insulation, you'll get slightly more heat loss through the walls. Unlikely you would be able to measure it without some very expensive test equipment.

Not likely to cause any issues when selling, and the insurance company wouldn't be interested. They would be more concerned about the type of insulation and the fire risk it posed - Rockwool is non-combustible, so poses zero fire risk.

Aside from BC paperwork, you really want a warranty covering the refurbishment against any defects.

Albermarle

 Year built: 1950 (from my understanding it is all solid brick apart from a recent extension that has cavity wall.)

That would be unusual, most houses were built with cavity walls from the round about the1930's onwards.

alwaysquestioning

Albermarle said:

 Year built: 1950 (from my understanding it is all solid brick apart from a recent extension that has cavity wall.)

That would be unusual, most houses were built with cavity walls from the round about the1930's onwards.

The EPC says this



How can I better understand this? I’m unsure whether the surveyor accurately identified the type of walls in my property.
Should I check with the estate agent or the seller? Or is there an online way to verify the wall type?

Albermarle

It is easily possible to identify a solid brick wall from the brick pattern. However if it is covered in insulation then that would not be possible.

FreeBear

Albermarle said:

It is easily possible to identify a solid brick wall from the brick pattern. However if it is covered in insulation then that would not be possible.

I have seen double skinned walls built with a flemish bond - A lot of extra work, so only really worth it if you have to match an existing wall or both sides are visible.

Measuring the thickness of the wall at a window or door reveal would give you a better indication - On this particular building, we have been told 50mm of insulation has been put on the outside. So allowing for plaster/render, the wall should be around 320mm thick.

alwaysquestioning

from my understanding looking at the brick pattern, this should be a solid brick wall, is it right?

luckily google street view holds on old photos of the streets/buildings.

What are those protrusions over the windows?

MikeJXE

I agree a solid wall

The tiles are a feature