Low profile insulation retrofit for screeded concrete floor and wall insulation upgrades

[saveasteading]

1 hour ago, abernabei said:

what do you think about using

- insulated cement boards

Look at Wedi boards. Strong insulation boards. 6mm to 20mm thick.

[abernabei]

thank you, that seems fairly strong.

 

Just found XPS is quite flammable though

Edited December 2, 2023 by abernabei

[abernabei]

would the Wedi board be suitable for installing right under laminate?

Or would it still require some kind of additional support layer?

[abernabei]

current options for floating floor are:

- 30mm XPS wedi boards, fire rating E   + underlay and laminate     (no height for adding plywood unless we decrease wedi to 20mm)

- 20mm PIR board, fire rating E + 18mm plywood (or 2x9mm plywood) + underlay and laminate

 

any reason to go for one or the other?

 

I'm tempted to go for PIR + plywood as I feel it might feel more solid despite the lower compressivity of the PIR

Edited December 12, 2023 by abernabei

[saveasteading]

Wedi is a stiff material and can be fixed down with pins or tile adhesive. Then can be walked on or tiled/ laminate.

Pir is cheaper but needs a hard board over it.

Without analysing further I'd be plumping for wedi.

[abernabei]

After going back and forth on what to do, I think I have settled on

 

• DONE: Epoxy DPM (already installed, Mapeproof OneCoat)
• 20mm PIR with fire rating E
• 18mm t&g plywood or 2 x 9mm plywood. The 9mm do not seem to be available with t&g, I guess because they're too thin.
• VCL? There are lots of people pro and against it, as it often happens it's not really clear what path to pursue
• underlay
• 12mm laminate

 

Regarding the VCL, there are 2 schools of thought:

1. "VCL is a must have": these people argue it is required to stop moisture from above condensing under the insulation layer, which makes sense...
2. "don't do it": these people argue the epoxy DPM and VLC on top of the insulation will create a plastic bag around the insulation and if any moisture were to get in between those layers (sealing the liquid DPM at the edges is virtually impossible, and the VCL might not be 100% sealed either) will get stuck there. These arguments make sense too...

 

Regarding the insulation layer: we ultimately decided against Wedi as we couldn't justify the higher price, considering their flammability and tile adhesive installation method (that's the only allowed installation method, as far as I could read on the official manual).

With Wedi we wouldn't need the plywood layer but it would lead to higher installation and material costs and higher risk in case of fire.

 

Any opinion on the proposed plan?

Edited January 1 by abernabei

[JohnMo]

You have a dpm, so not sure the vcl is actually what you are calling it. If you do add a polythene sheet it will effectively become a slip membrane to allow movement of the flooring above - a good thing and cheap to do

 

Either two layers of 9mm ply staggered joints glued and screwed or as specified 18mm.  The 2x 9mm with give a single piece floating floor. Both versions the floor should be made 10mm smaller all round than the room walls, so it floats and can expand and contract easily.

[abernabei]

4 minutes ago, JohnMo said:

You have a dpm, so not sure the vcl is actually what you are calling it. If you do add a polythene sheet it will effectively become a slip membrane to allow movement of the flooring above - a good thing and cheap to do

 

Either two layers of 9mm ply staggered joints glued and screwed or as specified 18mm.  The 2x 9mm with give a single piece floating floor. Both versions the floor should be made 10mm smaller all round than the room walls, so it floats and can expand and contract easily.

The DPM is a liquid one we installed on top of the existing screed as there did not seem to be any pre-existing DPM.

That is under the insulation and stops the moisture from below.

The VCL would be on top of the insulation and would the moisture from above. Is VCL the wrong term for it?

 

4 minutes ago, JohnMo said:

The 2x 9mm with give a single piece floating floor

What do you mean?

Edited January 1 by abernabei

[JohnMo]

21 minutes ago, JohnMo said:

Either two layers of 9mm ply staggered joints glued and screwed

 

18 minutes ago, abernabei said:

21 minutes ago, JohnMo said:

The 2x 9mm with give a single piece floating floor

What do you mean?

A layer of 9mm ply laid down, second layer on top with joint lines of the first layer overlapped by the second. Once glued and screwed together will become a single piece of ply 18mm thick. With staggered joints there are no weak areas. You make the ply floor smaller than the room so it can move (float) to allow it to expand and contract.

 

22 minutes ago, abernabei said:

The VCL would be on top of the insulation and would the moisture from above. Is VCL the wrong term for it?

Just add it, it's not doing anything as a VCL as there is nothing to protect from moisture. It's just a slip membrane to allow the insulation and ply floor to move independently of each other.

[abernabei]

37 minutes ago, JohnMo said:

 

A layer of 9mm ply laid down, second layer on top with joint lines of the first layer overlapped by the second. Once glued and screwed together will become a single piece of ply 18mm thick. With staggered joints there are no weak areas. You make the ply floor smaller than the room so it can move (float) to allow it to expand and contract.

cool, that was all clear, just wanted to confirm

37 minutes ago, JohnMo said:

Just add it, it's not doing anything as a VCL as there is nothing to protect from moisture. It's just a slip membrane to allow the insulation and ply floor to move independently of each other.

The idea would be to prevent any moisture from above from getting trapped between insulation and DPM, as the DPM is on the cold side of the floor. Does that make sense?

However, once the VCL is in place the new risk is moisture getting trapped in the DPM-insulation-VCL sandwich (the assumption is DPM and VCL are not fully sealed so moisture can still get in between those layers.

Edited January 1 by abernabei

[Ferdinand]

Does the @JohnMo idea give you depth to make your 20mm of insulation a bit thicker?

 

When I wanted to insulate above a (wooden, suspended) floor for a renovation for a tenanted property back in 2017-18 I did somethjng similar. I couldn't go down (but could do some underfloor insulation), and I was replacing doors without redoing door lintels etc.

 

My height limitation was that modern doors are not as trimmable as might be assumed. The best trimming margin I could find was ~60mm combined off top and bottom. *Watch this point* .

 

My layering was 25mm insulation board, slip membrane to stop allow movement / stop squeaks, 18mm OSB (gaps of ~6mm between sheet edges iirc), then underlay and carpet. I could have used Click Laminate (ie QuickStep as I always use) instead of carpet.

 

2 extra tricks I put in:

 

1 - I dealt with my carpet edges by using quadrant siliconed onto the skirting not nailed or glued - can take off with a Stanley knife. 

2 - I did 1 because I left an insulated well 300mm wide around the inside walls where I ran all my wiring for sockets and plumbing for radiators (which were also put on the inside walls) to reduce penetrations and keep everything inside the insulated envelope, and it all needed to be accessible.

 

I framed out my 25mm insulation using 25x38mm roofing laths - leaving the channels round the edge, and cut the OSB to match the framing, so that could just be lifted to get at wiring and plumbing I can't honestly remember if I screwed the OSB to the laths or just left it floating with the sheet edges aligned to the frame. One alternative to the "monolithic floating floor" is to frame out at the size of your laminate and put a thick strong laminate directly onto the frame; that will save a bit more height.

 

There is a thread about it here, which also covers other aspects - not all of which I did. The insulated floor worked and the (mid-high end) underlay and carpet still looks as good as new (change of tenant last August and they love it).

 

[abernabei]

Thanks @Ferdinand I had a good read at the linked thread good tricks!

In our case, the rewiring has already been started and it's going on the concrete ceiling (second ceiling to be built on top of that).

Heating pipes will run below the internal walls insulated plasterboard boards, as those are 62.5mm thick

 

We're having an ASHP installed, too, but unfortunately we couldn't go for UFH because of the big downward heat lost that would create (the concrete floor is not currently insulated).

 

Any reason why you used laths throughout the floor, rather than just at the edges to create the service channels?

 

In our plan there would be no laths

 

Which @JohnMo's idea are you referring to, Wedi boards?

It's a very valid alternative, it would give us comparable insulation saving perhaps 5mm of floor height (or less, depending on adhesive thickness) but it comes with a few disadvantages which I highlighted in my previous post.

Still a very good option though

Edited January 1 by abernabei

[JohnMo]

18 minutes ago, abernabei said:

We're having an ASHP installed

Concider getting fan coils instead of radiators, fine for heating and cooling. Smaller than a radiator, flow temps similar to UFH (35 degs). Faster response than a radiator due to fan assistance.

[abernabei]

1 hour ago, JohnMo said:

Concider getting fan coils instead of radiators, fine for heating and cooling. Smaller than a radiator, flow temps similar to UFH (35 degs). Faster response than a radiator due to fan assistance.

good call out...I'm a bit scared of opening another can of worms so late into the works 😅

I'll have a look, thanks

[Ferdinand]

3 hours ago, abernabei said:

Any reason why you used laths throughout the floor, rather than just at the edges to create the service channels?

A couple of reasons - one simply that laths come in 5m lengths and is inexpensive, so there was enough! And I decided since it was a rental it would make sense to protect the celotex everywhere rather than just by the door.
 

3 hours ago, abernabei said:

Which @JohnMo's idea are you referring to, Wedi boards?

I was referring to this one below, but I think I misunderstood slightly in that it does not save depth over a single 18mm thickness; what it does is make it monolithic.
 

8 hours ago, JohnMo said:

A layer of 9mm ply laid down, second layer on top with joint lines of the first layer overlapped by the second. Once glued and screwed together will become a single piece of ply 18mm thick. With staggered joints there are no weak areas. You make the ply floor smaller than the room so it can move (float) to allow it to expand and contract.

 

[abernabei]

@Ferdinand I think I am going to go with your plan!

Which VCL did you install?

[Ferdinand]

For that if I recall I just used a normal clear roll, perhaps something like this, which is 4m wide when unfolded so it will do many rooms and lap up at the sides in one piece if you need that:

https://www.screwfix.com/p/capital-valley-plastics-ltd-general-purpose-sheeting-clear-150ga-25m-x-4m/71880

I'd suggest going down to Screwfix and having a look to make sure you think it is strong enough.

If not there are thicker ones available.

If you need to overlap, then you can do it by say 0.5m and tape along the join if you think that matters.

One rough check that your subfloor is properly dry is to tape a square of sheet to the surface, leave it for a couple of days and see if any moisture  which has been evaportating into the atmosphere has collected underneath.

 

One thing to remember is that if you have one lapped up at the sides, the first lot of water from any leak you have isn't going anywhere unless you have slits - which may be good or bad depending. But leaks are very rare. I get less than one per 50 years of house occupancy in my small set of rentals.

[abernabei]

Thank you, and did you screw through the VCL when installing the OSB?

It seems like a big no-no, but alternatives are either putting the VCL on top of the plywood (though every best practice document says it should be right on top of the insulation) or laying the plywood without screwing it to the battens, which I fear will decrease its stability.

 

We went with the battens approach as that will allow us to use phenolic foam instead of PIR, and even though there will cold bridges due to the battens, the overall gain should be positive, or at least that's the bet.

 

Laying a floating floor directly on top of PIR (140kPa compressive strength) didn't really convince me, after seeing first hand the 120kPa strength phenolic foam K103 behaves under pressure.

 

(we spoke about the other alternative, wedi boards, a few posts up)