ICF vs Precast Insulated Panels

[MariaD]

Hello everyone,

I find myself in a dilemma between choosing ICF or Precast Insulated Panels for the construction of my new house, specifically for external walls and floors. While I lean towards precast insulated panels, some questions remain unanswered. I plan to build a 2-storey house with internal dimensions of 8.5m x 8.5m, intending to make the attic 'habitable' with a spare room and utility space. I'm also considering raising the walls by 0.5m, essentially making it nearly a 2.5-storey structure. Additionally, I am contemplating a roof pitch of either 8/12 or 7/12. Here are my questions:

Can anyone provide an estimate of the potential differences in cost and completion time between ICF and precast insulated walls?
For the external rendering of precast insulated walls, is it sufficient to paint the concrete, or is another type of rendering (such as stucco) necessary? If rendering is necessary, what would you recommend for optimal durability and maintenance? Should a membrane be installed between the concrete and rendering to prevent trapping humidity/water?
Concerning precast insulated walls, is rendering needed on the interior side, or is it possible to paint the concrete directly?
Regarding the floor, if I opt for hollow core slabs, are load-bearing walls necessary on the ground floor, considering a span of 8.5m from wall to wall? How thick would the floor be approximately?
I appreciate any insights or advice you can offer. Thank you.

[Conor]

I doubt that precast insualted panels are a standard construction method recognised by lenders and insurers. ICF can be hit and miss even though it's fairly common now.

 

Explored any other options? Timber frame with block skin for example?

 

For the floor spans you are talking you'll need some steel in there to take the spans, a 150mm hallowcore plank typically spans about 5-6m max.

 

Have you spoken to an architect or SE yet? Don't get stuck on details until you've the big stuff sorted.

[saveasteading]

For precast plank floors remember that you need artic and crane access. For 8m span they'll be about 200mm thick then insulation and screed above.

 

I agree that considering the build method is worth considering early, but also that there can be too much detail.

 

Can I ask what draws you towards precast panel walls? I'm not against it, but it wouldn't be my first choice.

 

2.5 storeys is tall and skinny. 

Where are you with planning permission?

[MariaD]

9 hours ago, Conor said:

I doubt that precast insualted panels are a standard construction method recognised by lenders and insurers. ICF can be hit and miss even though it's fairly common now.

 

Explored any other options? Timber frame with block skin for example?

 

For the floor spans you are talking you'll need some steel in there to take the spans, a 150mm hallowcore plank typically spans about 5-6m max.

 

Have you spoken to an architect or SE yet? Don't get stuck on details until you've the big stuff sorted.

Thank you very much for your response. I am open to exploring all options in theory. My priorities, in order, are durability, low maintenance, construction speed, noise reduction, and simplicity. While I understand that a timber-built house has the potential to last for centuries, my concern lies in the perceived higher maintenance requirements. Additionally, timber frames may perform less effectively in noise insulation. During storms, there might be vibrations in a timber-framed house, especially if opting for a timber floor, which is known to be noisier.

In comparing masonry to methods like ICF or precast insulated panels, I assumed that masonry would take more time to build, considering the scarcity of labor in the sector. Another consideration is that ICF is simpler to construct and provides complete airtightness, while precast panels are manufactured in a factory. Consequently, these two options seem less risky to me, although I acknowledge that my perception might be inaccurate.

If I were to contemplate masonry, I'd likely explore a single-leaf method using aerated concrete blocks. However, I've encountered criticism regarding these blocks being 'brittle' and prone to damage when exposed to humidity. SIP, while an option, presents similar disadvantages to timber frames. I want to clarify that cost is indeed a factor, but I would prefer to invest in the best building method that aligns with all my requirements, even if it comes at a higher cost than other alternatives

Edited January 24 by MariaD

[MariaD]

9 hours ago, saveasteading said:

For precast plank floors remember that you need artic and crane access. For 8m span they'll be about 200mm thick then insulation and screed above.

 

I agree that considering the build method is worth considering early, but also that there can be too much detail.

 

Can I ask what draws you towards precast panel walls? I'm not against it, but it wouldn't be my first choice.

 

2.5 storeys is tall and skinny. 

Where are you with planning permission?

Thank you very much; the considerations you provided are highly valuable. The reason I am inclined towards precast panel walls, as explained in the previous post, is because it appears to meet all my requirements: durability, low maintenance, construction speed, noise reduction, and simplicity. Additionally, I neglected to mention that I am aiming to achieve, or at least come close to, a passive standard for the house. While I may not seek actual certification, I aspire to attain similar performance levels. Concrete's superior heat absorption is another advantageous factor.

As for planning permission, I have not obtained it yet. However, the land I purchased is located in a residential-zoned area surrounded by other two-story houses. The envisioned height for the house I am currently designing will not exceed 9.2m, staying within the range of the neighboring houses. I had a pre-planning session, and the individual I consulted with assured me that the height would not pose any issues.

I'm not aiming to finalize all the details at this point, but I would like to have a clear understanding of my preferences and potential considerations. Given your apparent knowledge of concrete, what, in your opinion, would be the optimal method for constructing a concrete floor while minimizing both thickness and weight?

[Mr Punter]

If you have internal load bearing walls the hollowcore planks or beam and block would work fine.

 

A well designed timber floor can also work very well and would meet your criteria, additionally allowing a greater choice of structure type.

 

It is best to get an approved design, then decide what performance you require (insulation, low noise transfer, construction speed, maintenance, durability, environmental impact, price etc.) before deciding on structure type and build method.

 

 

[Conor]

Good point about labour. However, doing something niche life precast panels or ICF, will reduce the potential pool of contractors even further. You want the right people for the job. 

 

Re build speed.. yes on paper it's faster, but I think a bigger factor in construction time is how good your builder is, how you package the works, and how organised you are. The method is secondary tbh. Our ICF guy buggered off on several occasions for days / weeks on end as he has two crews building six houses at the same time. So it took a full nine months to go from slab to roof ridge with the ICF. You could have a good, organised builder using block and brick that could have a shell up in three months. Oh, and the Internal works and second fixes take up approx 2/3 of the build time, while the slab /walls etc are about 1/3. We waited 6months for windows alone.

 

Finally, keep it simple, don't reinvent the wheel.

 

If I was building again, I'd probably do timber frame with block skin. Mainly for sustainability/ Carbon reasons, but also it's what the industry does here, and there's better availability of skills and knowledge.

[saveasteading]

4 hours ago, Conor said:

keep it simple, don't reinvent the wheel.

Houses are the shape they are for very good reasons, mostly keeping the weather out. 

Any variations such as flat roofs, fancy shapes and novel materials are a cost and a risk.  Go for it if you've plenty of budget and don't mind some problems.

[SteamyTea]

With any modular or off site building method, you are taking a huge financial risk.  There have a been a few people on here that have been caught out to the tune of several £10ks.

 

Masonry is alright, but rather old fashion and not very airtight.

 

Stick build on site would give you the greatest flexibility and your 'noise' fears are really down to the design, not the material.

 

Both masonry and timber work do rely on having the right skills in your area.

 

17 hours ago, saveasteading said:

Houses are the shape they are for very good reasons

Furniture fits them better.

[MariaD]

13 hours ago, SteamyTea said:

With any modular or off site building method, you are taking a huge financial risk.  There have a been a few people on here that have been caught out to the tune of several £10ks.

 

Can you please expand on that? What was the reason for that (i.e. supplier went out of business?)

[MariaD]

On 24/01/2024 at 20:29, Conor said:

Good point about labour. However, doing something niche life precast panels or ICF, will reduce the potential pool of contractors even further. You want the right people for the job. 

 

Re build speed.. yes on paper it's faster, but I think a bigger factor in construction time is how good your builder is, how you package the works, and how organised you are. The method is secondary tbh. Our ICF guy buggered off on several occasions for days / weeks on end as he has two crews building six houses at the same time. So it took a full nine months to go from slab to roof ridge with the ICF. You could have a good, organised builder using block and brick that could have a shell up in three months. Oh, and the Internal works and second fixes take up approx 2/3 of the build time, while the slab /walls etc are about 1/3. We waited 6months for windows alone.

 

Finally, keep it simple, don't reinvent the wheel.

 

If I was building again, I'd probably do timber frame with block skin. Mainly for sustainability/ Carbon reasons, but also it's what the industry does here, and there's better availability of skills and knowledge.

 

Thanks a lot for the valuable information you shared. It's particularly helpful to know that internal works and second fixes account for approximately two-thirds of the project.

Could you share your preference for timber over SIP? SIP was one of the alternatives I was considering, but I'm facing challenges in finding a manufacturer that produces SIP with OSB4 panels.

Did you have any issues with ICF after the house was built? Does it require any maintenance?

 

Anyway, I'm going with a design as simple as possible.

Edited January 26 by MariaD

[SteamyTea]

39 minutes ago, MariaD said:

14 hours ago, SteamyTea said:

With any modular or off site building method, you are taking a huge financial risk.  There have a been a few people on here that have been caught out to the tune of several £10ks.

 

Can you please expand on that?

 

[Nick Laslett]

The success of any build method is rather dependent on who is doing the build. Do you want low cost, or high quality or quick execution. You can’t have all three. 
 

I wanted the simplest build process I could get. My ICF supplier Thermohouse was happy to do the build as well. I think this is very much location dependent. They have a flooring product, which is also poured concrete. They will do a poured concrete stairs as well.  They also have a roofing product, and an in-house structural engineer. They designed and installed the roof steels. 
 

The good news for me was that gave me a finished shell relatively quickly. I only had one person to deal with, and the same crew of three guys did all of the work. The whole process was very straightforward. They gave me a fixed price, with phased payments.

 

There is a big but, ICF is just not a common build method in UK. You won’t get follow-on trades familiar with this system. Unless you are very confident on how to finish the shell, there are a lot of potential problems that won’t be solved optimally. I knew that I was going to be doing all this work, so it was not a problem for me. 
 

Going into my self build I prioritised the build method over execution. It is probably more important to figure out who is going to do the build and work to their strengths. If you have a builder with a lot of experience with Precast Insulated Panels then that approach could work. 

[saveasteading]

1 minute ago, Nick Laslett said:

You can’t have all three. 

That's often said. It's relative though.

With a practical design, good builders and good management it will be faster , better and cheaper than without.

[Bancroft]

Might ICF panels be a mid-way option for you?

 

 

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