abernabei Posted January 20 Share Posted January 20 Hi everyone, we're about to install some insulation on top of a solid concrete floor. Context: Ceiling height is already very low, so we've got very little space to play with. We've decided to go with the following build-up: - existing concrete - DONE: liquid DPM (mapeproof onecoat) - 25x38mm battens, 40cm spacing between centers. This is to increase stability of the insulated floor (alternatives like PIR and wedi boards were discussed at the linked thread) - 25mm Kingspan K103 phenolic board - VCL? - 18mm SpruceFloor plywood - VCL? (alternative position) - underlay - 12mm laminate (most likely QuickStep Impressive Ultra) to gain additional stability There are a few challenges which I would like to get your opinion on: any advice on how to merge the liquid DPM with the existing DPC? The DPC is very short (60s maisonette in an ex-council block) and neither Mapei nor Ardex mention this challenge in their technical documents. Haven't contacted their technical teams about this matter, yet. given we're going with battens, the plan is to screw and glue the 18mm plywood to the battens. Installing the VCL below the plywood would mean screwing through it to fix the plywood in place, which doesn't seem like a great idea. Is that how it's usually done? I read a number of documents on insulated suspended timber floors but they never mention how the floorboards are then fixed to the joists without perforating the VCL underneath. Would it make sense to install the VCL above the plywood? The kitchen is already in place and we will not be able to Installation guides for the VCL recommend lapping 10cm on the walls, which makes sense but... Where is that taped if the wall is already built? On the finished wall? If so, how would you then install the skirting board on top of it, assuming the VCL will already cover 10cm height from the floor? Nailing the skirting board in place, perforating the VCL, doesn't sound like a good idea...but at the same time you cannot glue the skirting board to the VCL, as that's just taped to the wall... The only option I can think of getting a 15cm tall skirting board and then glueing it in place using the top 5cm or less which are above the VCL... How do people usually workaround that limitation? Does anyone have experience with similar projects? Link to comment Share on other sites More sharing options...
Redbeard Posted January 20 Share Posted January 20 Similar issue to when you are installing PIR below rafters with timber cross-battens over the PIR. One schoolof thought says that a hoile with a screw in it is not really a hole, and another says 'yes it is' and guns silicone into a pre-drilled hole to give each screw a 'silicone VCL grommet'. I have never used phenolic in a floor before but I have used PIR with T & G OSB overlaid with a VCL (well, thick DPM, in fact, but acting as a VCL) between, as a floating floor. No weakness detected in several years' use. Reason for the thick DPM is so that your big work-boots don't kick holes in rather wimpy thin VCL. Link to comment Share on other sites More sharing options...
abernabei Posted January 20 Author Share Posted January 20 thanks for sharing that 👍 I'll be honest, I did think about the silicone Link to comment Share on other sites More sharing options...
Roger440 Posted January 20 Share Posted January 20 Butyl tape. Apply this where you intend to "puncture" the VCL. Problem fixed. Certainly standard procedure when putting a VCL on wall. Just done it my workshop. Link to comment Share on other sites More sharing options...
abernabei Posted January 20 Author Share Posted January 20 (edited) so apply butyl tapes all along the battens wherever we intend to screw the boards down? (30cm spacing on long edges, 15cm on short edges, SpruceFloor recommendations) Do you mean the double-sided one, with the idea that it will kind-of seal the hole once the screw is in? For a similar reason, installing the VCL below the plywood means I wouldn't be able to glue the boards down to the battens to increase stability we have done that on first floor (screwed and glued, no VCL) with excellent results, but it seems like that won't be an option, if the VCL has to be below. Edited January 20 by abernabei Link to comment Share on other sites More sharing options...
Roger440 Posted January 20 Share Posted January 20 4 minutes ago, abernabei said: so apply butyl tapes all along the battens wherever we intend to screw the boards down? (30cm spacing on long edges, 15cm on short edges, SpruceFloor recommendations) Do you mean the double-sided one, with the idea that it will kind-of seal the hole once the screw is in? For a similar reason, installing the VCL below the plywood means I wouldn't be able to glue the boards down to the battens to increase stability we have done that on first floor (screwed and glued, no VCL) with excellent results, but it seems like that won't be an option, if the VCL has to be below. Yes i used the double sided. I may be misunderstanding, but why not put VCL UNDER the battens? Or, actually, why are you using a VCL as you have put a DPC in already. Or are you worried about condensation forming within the floor build up? Seems unlikely and thus overkill? 1 Link to comment Share on other sites More sharing options...
abernabei Posted January 20 Author Share Posted January 20 (edited) All the documents I could find recommend installing a DPM below and a VCL above the insulation (especially for vapour closed setups) to prevent moisture from reaching the insulation and getting trapped between insulation and slab. I could be missing or misunderstanding something though Edited January 20 by abernabei Link to comment Share on other sites More sharing options...
Iceverge Posted January 21 Share Posted January 21 I think you're massively over engineering this. 25mm PIR sheets taped at the seams, and foamed to the walls. 2* layers of OSB floating on top, glued and screwed. Leave an expansion gap at the perimeter. Laminate flooring. I can't see a DPM or VCL achieving anything in this case. Link to comment Share on other sites More sharing options...
abernabei Posted January 21 Author Share Posted January 21 (edited) Heh, I wish it were that easy so many conflicting opinions around... manufacturers recommend adding battens in places where a high load is expected. I don't want to risk the floor slightly sagging over time because I add a heavy load in a place that was previously unsupported, hence why we're going with battens. Regarding the OSB, by "glued and screwed" you mean between them? (or where is it screwed to, if it's floating on top?) Regarding VCL, please see the following for an example, they all specify a VCL above insulation, below OSB/plywood/floor https://www.kingspan.com/gb/en/knowledge-articles/a-guide-to-constructing-a-floating-floor/ https://assets.publishing.service.gov.uk/media/62a0683ad3bf7f036fc493ba/solid-floor-insulation-best-practice.pdf https://polyfoamxps.co.uk/floor-insulation/concreate-slab-insulation/ https://www.permagard.co.uk/advice/installing-vcl-vapour-control-layer Edited January 21 by abernabei Link to comment Share on other sites More sharing options...
Iceverge Posted January 23 Share Posted January 23 On 21/01/2024 at 09:10, abernabei said: Heh, I wish it were that easy so many conflicting opinions around... manufacturers recommend adding battens in places where a high load is expected. I don't want to risk the floor slightly sagging over time because I add a heavy load in a place that was previously unsupported, hence why we're going with battens. Regarding the OSB, by "glued and screwed" you mean between them? (or where is it screwed to, if it's floating on top?) Regarding VCL, please see the following for an example, they all specify a VCL above insulation, below OSB/plywood/floor https://www.kingspan.com/gb/en/knowledge-articles/a-guide-to-constructing-a-floating-floor/ https://assets.publishing.service.gov.uk/media/62a0683ad3bf7f036fc493ba/solid-floor-insulation-best-practice.pdf https://polyfoamxps.co.uk/floor-insulation/concreate-slab-insulation/ https://www.permagard.co.uk/advice/installing-vcl-vapour-control-layer Yup glued and screwed to itself. All joints broken between the layers. If you tape the foil faces of the PIR then another layer of a material of low permeability is pointless as far as I can see. In fact there's a risk with two layers of impermeability materials as any construction moisture will be trapped permanently. As the battens and PIR have different compression strengths I would worry moreso that they would compress differently over time and sags would be more obvious. You could have very closely spaced battens I suppose but then you're really eating into the insulative effects. Also you'll have to rip 25mm battens from larger materials as they come typically in 22mm so all the weight will be on the insulation anyway if you use them. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted January 23 Share Posted January 23 https://youtu.be/qyUZ3SgNvfY?si=oUlP9rCa8zV_Wwch Nice video here although he screws though to the subfloor. I'd prefer to leave it floating. Link to comment Share on other sites More sharing options...
Annker Posted January 28 Share Posted January 28 On 21/01/2024 at 09:10, abernabei said: Heh, I wish it were that easy so many conflicting opinions around... manufacturers recommend adding battens in places where a high load is expected. I don't want to risk the floor slightly sagging over time because I add a heavy load in a place that was previously unsupported, hence why we're going with battens. Regarding the OSB, by "glued and screwed" you mean between them? (or where is it screwed to, if it's floating on top?) Regarding VCL, please see the following for an example, they all specify a VCL above insulation, below OSB/plywood/floor https://www.kingspan.com/gb/en/knowledge-articles/a-guide-to-constructing-a-floating-floor/ https://assets.publishing.service.gov.uk/media/62a0683ad3bf7f036fc493ba/solid-floor-insulation-best-practice.pdf https://polyfoamxps.co.uk/floor-insulation/concreate-slab-insulation/ https://www.permagard.co.uk/advice/installing-vcl-vapour-control-layer I've installed hardwood timber floors in many houses using the floating floor method and it performs exceptionally well. I actually revisited a house over christmas where this was done in 2006 and the home owners reported the floors are as stable as the day the were installed, I believe 17/18 years is a sufficient test duration! I believe the buildup was: 18mm oak T&G boards 12mm hardwood ply (laid half bond at a 45 degree and screwed to the ply layer below) 12mm hardwood ply (laid half bond and loose over the PIR) 120 PIR Sheet DPM Concrete subfloor 1 Link to comment Share on other sites More sharing options...
Alan Ambrose Posted January 28 Share Posted January 28 (edited) Ah interesting, I think sometimes we go overboard ‘fixing’ things to other things when actually gravity will do the job fine. What kind of gap did you leave at the edges for expansion etc? By ‘hardwood ply’ you mean construction grade rather than actual marine sapele or something? Edited January 28 by Alan Ambrose Link to comment Share on other sites More sharing options...
Iceverge Posted January 28 Share Posted January 28 As a mere human it's hard to tell the difference between compressive strength and surface hardness. Just because you can dig your nail into a material doesn't mean it's not plenty strong enough to hold up a house. Infact the insulation can often be stronger than the soil below it. 1 Link to comment Share on other sites More sharing options...
Annker Posted January 28 Share Posted January 28 9 hours ago, Alan Ambrose said: Ah interesting, I think sometimes we go overboard ‘fixing’ things to other things when actually gravity will do the job fine. What kind of gap did you leave at the edges for expansion etc? By ‘hardwood ply’ you mean construction grade rather than actual marine sapele or something? 10mm gap along both plywood to plywood junctions and the perimeter of the room. Plywood doesn't expand along the length or width of the sheet to any degree that requires consideration in this scenario. I used Hardwood faced ply as opposed to softwood faced shuttering ply. In the absence of the floor having any direct fixing to the underlying substrate, it is prudent to lay up the subfloor with materials that remain general flat rather than warp if you look at it sideways like shuttering ply The floors I was installing were generally all hardwood T&G flooring, secret nailed and occasionally may have some inlay work. And for that particular installation I would rate plywood above OSB. I feel plywood has a more robust surface for installation; nailing, marking out on etc. Link to comment Share on other sites More sharing options...
Annker Posted January 28 Share Posted January 28 6 hours ago, Iceverge said: As a mere human it's hard to tell the difference between compressive strength and surface hardness. Just because you can dig your nail into a material doesn't mean it's not plenty strong enough to hold up a house. Infact the insulation can often be stronger than the soil below it. Exactly this. Sure the entire world is sitting on liquid molten material and its going nowhere (save a few earthquakes!) Link to comment Share on other sites More sharing options...
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