The breathable membrane has to go all the way around the room and go slightly up the wall or it's marginally better than using chickenwire. You also need to tape the seams and the batons at the bottom of the timbers are really not optional. It also looks like you cut the Rockwool too loose as it should be hard to push it and slightly compressed agains the timbers. Overtime, houses move and your insulation has to stay in place with movement. Batons are there to make sure the membrane does not separate and the membrane has to be a taped in order to ensure that wind stays on the outside of your heated envelope. Most of all, given the disruption that working on your floors causes, you really want to make sure you don't have to open then up again for a long time.
This is exactly the video I needed I’m currently trying to insulate my floor, my room is about twice as large as the room you have done in the video. How much breathable membrane did you buy? 1.5m x 15 meters?
By far and away the best demonstration of installing under joist insulation I have seen. Simple, accurate and practical-just what we all need. Well presented and carried out sir! 👍👍👍👍👍 I now feel ready to take on our old bedroom at the back of the house…..thank you for posting this 🙏
I have quite a deep subfloor, as is common in scotland, so did it from underneath. Was amazed by the difference, especially because I have exposed floorboards! I reckon mine will pay for itself in 1-2 years simply through draft reduction.
@@AliDymock I think it's related to the relative position of the frost line, which is much deeper in Scotland. In Aberdeen I had a full size full height basement
@@GM-dc8vr I have a similar thing in the south in England but I think its due to the house being a weird hodge-podge built up over the last few hundred years on different levels. Can confirm it is very draughty and cold.
Hi - is it 100% necessary for the VCL? I am doing it from below now and can’t rip the boards up… I have had a fair bit of advice from both Building Control and the insulation manufacturer that it’s not necessary… thanks, great video btw
Good video , is there any risk of damp between the 2 membranes ? So the non breathable membrane on the top of the floor boards, that won’t trap moisture will it ?
I have a house from 1939 in Poland. Same floor. I thought I would pad the membrane under the beams and then pour in granulated Styrofoam. Styrofoam would be free from construction. I wanted to grind it with a machine. Regards
You should knife small slits into each run of the vapour barrier, at, say, one foot intervals. If a catastrophically burst pipe floods this floor the slits will allow the water to drain through. Without the slits the water - which could be tonnes - will give you a forever pond, on top of the vapour barrier, just under your flooring. Tiny slits will not compromise the vapour barrier.
Nice clear video thanks. I have a 1930s house and the boards are difficult to get up and split. I can get up about every 4th one as they have been lifted and ruined in the past. I did use the same type of insulation on my roof sliding bits into the small slope so I am thinking I can do similar sliding the bats into the floor area. I am just thinking that a laminate floor will be air tight and the black dpc is also air tight so the boards are stuck in the middle with no air. So I think I would leave out the black dpc, let the boards breathe and any floor covering will stop drafts.
Very informative video, and tells you pretty much all you need to know in only 6 minutes. I think the only thing missing maybe is how to get the flooring and floorboards up, but appreciate everything else nonetheless.
I did the same. Massive difference. I’m still surprised why people in the UK build houses this way. This should be concrete panels not wood. If it is concrete no air ventillation is required. This technology is 200 years behind the civilised world.
Sure, but sometimes suspended floors are still needed, not only are they cheaper and faster, if the ground is poor and the building requires piled foundations, you won’t be allowed by building control to install a ground bearing slab. A simple solution to this is suspended timber. Also, if you are in an area with high shrinkage clay ground, and you remove a mature tree as part of some extension work, building control may also be requesting timber floors to offset the risk of ground heave.
Concrete floors actually have worse u-value than a well insulated suspended floor. That is because concrete conducts heat. You can of course put PIR or other insulation on top of concrete, but that has to be done at the right time and can't be retrofitted.
That makes a lot of sense. Wish I'd looked into that but perhaps the thing to do is take out the clay air brick as Azza said, from the outside and replace with a plastic one. Even if I had put some kind of duct in, it would have been difficult to seal around the sides so better if it's an all in one. Good tip 👍
Just push in a plastic duct from inside the house through the cavity to meet the external air brick, and ideally seal it against it. Plastic air bricks look terrible, never replace for plastic!!
@@AliDymock If you look very carefully at your video of the air brick you can see what the insulation installer has done. (look closely at the insulation and you can just see the blown fibre to the right-hand side which is slightly lighter in colour) When insulating a subfloor the air bricks are removed then Roll insulation is cut into strips and put into the cavity to stop the blown fibre from blocking the ventilation, a new air brick is then fitted. There is no need for a plastic sleeve in this situation. One other observation regarding the sub-floor insulation if you do it again, is to try and keep the insulation slightly above the joists by a few mm. This will ensure the insulation is tight against the floorboard. The basic rule of insulation is to keep the insulation as close as possible to the heat source.
Hi Ali, Looking to do this myself. Any reason why you didn't use PIR? Could I potentially use that instead? Also If I were doing the entire ground floor, would insulating then concreting over it be plausible? Would I still need air bricks in a concrete covering?
So the question is… can you notice a difference between this and other floors not insulated for drafts and also under your feet thermally ? Many thanks
I did mine using Kingspan PIR, only 50mm not the recommended 75mm, and yes its expensive (£600 for a room inc. new joists, batons, fixings, foil tape etc) but it paid for itself within 2 years in reducing heating costs.Absolute no brainer. The rock wool won't be as effective and you have to install a membrane which isn't necessary with the PIR boards. With material prices as they are now I would have to weigh it up carefully. I will not hesitate, personally, to PIR insulate any suspended floor in any future property. It makes a HUGE difference - especially if you also brick up any open chimneys (leaving an air brick at ground level under the insulation for ventilation).
I have been researching on how to insulate my suspended timber floor for a while now. Each time I come across a new tutorial on youtube I learn something, but I also get confused. Now I have got so many questions! For example 1 arent the membranes (both the dm and the vl) supposed to be sealed all around the room? And where should they be sealed, exactly? On the plasterboard under the skirting board, or on the bare wall under the plasterboard itself? 2 isn't the air vent at the level of the joists making the insulation much less efficient? Cause this is exactly the same situation I have in my house, and after watching other videos I thought that the entire perimeter of the room (at leqst esternal sides) should be sealed. The air vent being in the middle of the way is clearly an impediment to this. I don't know if I am clear, but I hope someone would help me
Brilliant idea using membrane , I was thinking of doing this but struggling to think how to keep insulation in place ( I was gonna use plywood) but your method seems then times easier ! We’ll done
Great job as usual Ali, if you used PIR would you leave the DPM/vapour barrier? I have leftover 100mm loft insulation, woukd this be as effective as rockwool batts? Thanks 👍🏻
Some will argue that the foil coating of the PIR can be considered a vapour barrier and a separate one is therefore not needed. However, any damage to the foil coating of the PIR will undermine it's effectiveness. Therefore, it's common to also lay a separate vapour barrier over the PIR.
@@mattrgee If you look manufacturer guide for installation no separate barrier is needed. Because material itself is also vapor resistant in some point and there is also PIR boards that has paper instead foil and even those doesn't need separate barrier.
What we should be doing to all properties but imagine, the family has to decamp into temporary accommodation, their furniture into storage, the workmen move in and once the boards are up startfinding pipes and dodgy wiring that all has to be sorted. The scale of the problem of net zero isn't understood by politicians but is by plumbers, heating engineers, electricians and builders. Good job.
It doesn't seem like it's worth it but I think I'll need to live in the house through one winter to determine. I'm going to delay putting in flooring until next year (buying a 1900 Victorian terrace). This is a really excellent DIY video if I do decide it's needed and I might do it anyway if I need to replace the joists - thank you!
This is on my to do list for my downstairs rooms. Place is so cold. In the mean time, we broke ground on the garden room and the concrete goes in on Wednesday.
Great stuff Robbie! Yeh I’ll be insulating the rest of the ground floor one room at a time to keep me sane. Worth doing with gas prices where they are currently…
Good vid. One question. Did you do anything with building regulations at all for this? I would assume that 100mm insulation of this sort would not be sufficient to meet the U value required?
Great video thanks. Just what i needed to see. I'm about to do exactly the same in a north facing very cold room with large windows in a 125 year old house. Hopefully this will make a big difference. Even in summer the carpeted floor is cold due to the ventilation underneath. I'm confused over the DPM though. 1 - Why is it needed and what is the source of the moisture it is protecting against? 2 - Will it not trap moisture immediately below it, which could then compromise the joists? Same job to be done on the kitchen, also north facing which has the same sub floor cold issue. However this one has a porcelain tiled floor with underfloor electric heating installed. Freezing to bare feet without the heating on. There's a good deep crawl space under this one accessible from the hall so will cut the rockwool slab tight to the joists then fix the breathable membrane to the bottom of the joists. Looking forward to warmer feet. Thanks.😀
I would like to know this also! I have recently insulated my suspended timber floor the same way as Ali here, with a vapour barrier on top of the joists, but I am worried about trapping moisture from leaks and spills etc between the Vapour barrier and the underside of the chipboard, Leading to mould or rot. Amazing how many differing opinions you find online. I wish I had not put in a VB now as I feel it is more likely to cause issues than prevent them. But what the hell do I know?
The Rockwool insulation in this context is a poor insulator, you would have been much better off with 100mm PIR foam board. The issue that will arise is one relating to a future EPC. The Govt are becoming more aggressive about bringing the housing stock up to scratch to meet climate change. The latest requirement is that all private landlords are to bring their properties up to Band C. I have a converted 1960's bungalow that the EPC recommendations for Band C include insulating the floors, presumably up to current standards, which is generally taken as using 100mm PIR board. This will be a mega hassle i.e. expensive as you can probably perceive. I will predict that at some point the Govt will insist that all domestic properties will have to achieve probably Band C especially when selling. It would make sense therefore to meet the best standards, whenever a major exercise like your refurbishment happens rather than do it for a second time later. In the meantime you will get the benefit of the improved insulation.
Hi Ali, great video. I have some questions and i hope you can answer 1. Is there any reason why you didn't cover the space between the insulation and joints with insulation tape? 2. In a part of the video you specify to leave space between the window and the insulation. Why? 3. Would it be possible to add a second link for the breathable membrane, as the one listed has expired? Thanks
We have a suspended timber floor in a 1930s house. We ate goung to put a solid wood floor on over the floor boards, with suitable underlay. Will insulating under the floor make a difference? Is it worth it?
Thanks for this. Planning a renovation and can't get round the guilt I am going to feel every time I look at the parquet unless I insulate first. You make it look almost easy to DIY... I would mention... wiring. I also have to rewire. Before or after the insulation?? Especially with the hammock method. Electrician would prefer before, but future electricians would prefer it on top, no?
I've made do with few and cheap tools in the past but having the right ones does make it easy and relatively quick - you got this! I would say to do the electrics before insulating and just make sure you have all the sockets you need so you won't have to add ones in future. Cables under the floor rarely need much attention.
Did you find any noticeable difference acoustically in the room after insulating? I’m considering doing the same, but my living room floor booms and echos when my kids jump up and down…..hoping this may help with that problem also
This sounds more like reverberation within the room itself where noise is bouncing off hard surfaces like laminate flooring walls and so on. This can be reduced by installing a carpet or if a wooden floor is to remain soft furnishings, rugs, cushions, foam absorber panel artwork on the walls. The only way to reduce the noise.
My house was built in 1908. It’s a semi and has been underpinned. There are air vents around the house. Will my house have normal floorboards? I really want to insulate.
At 2:20 you mention the membrane was placed face down but didn't expand on it. Is this because the membranes are designed to be face up in roovers, therefore the printed side should face out of the building?
Dunno what that black plastic was but what i have heard that those aren't allowed to use interior. We have one type of vapor barrier here and it's slight tinted for blue and you can still see through it. Usually that black stuff smell awful so it might be reason that it has made something not so healthy.
Thanks for this, it's brilliant and you make it seem so easy. Question, any idea of the durability of the breathable membrane to withstand "mouse attack"?
It’s crazy how we poles still come to work here in but our garden sheds are build better that houses in UK. Empty floors and walls that you can’t hang ikea frame 😀
Hi Ali, You seemed pleased to find insulation in the cavity. Do you have any reservations about the potential of damp with it? I inherited it with two of my houses, the one I'm doing now I'm doing my very best to remove it all.
Oh really? Well this side of the house has been built longer than I've been alive and no damp that I can see so yeh I was happy to find it. Surely cavity wall insulation is desirable? How and why are you getting it out, sounds like a story there...
@@AliDymock Hi, thanks for the reply. My house is a 1960s red brick bungalow, the construction looks identical to yours with the underfloor ventilation etc. The cavitys have been pumped with glass fibre insulation, on the west side that gets all the weather, the insulation is completely saturated. Even a few spots on the dryer side are also wet. My preference is to have the air gap in the cavity and we'll insulate the interior walls. It been hell of a Job to remove it, luckily we're starting a wrap around extension so we can gain access to 1/3 of the cavity, the rest of it will come out by removing the windows and popping holes in the brick work all the way around and fishing it out with a wire hook. I'm slightly envious your insulated cavity doesn't have the same issue! This was a great video BTW, we will definitely be doing under our timber floors with the same method!
@@aledjonesccc Glass fiber insulation has the same problem in wall cavities that it does in attics and other areas when it gets wet - it retains water. The issue is not likely to be the insulation, that's a more of a symptom of water ingress either from a damaged/missing cavity top plate/leaky roof and blown render on the outside. It's one of the reasons PIR and Rockwool are preferred on new builds and why the polystyrene balls are more often used as retrofit insulation.
@@AliDymock Yes in general CWI is a good thing but in my experience there are real potential problems with it, and many people don't know about them - again in my experience, but mainly because the CWI industry is just an awful collection of sharks and blaggers who'll say anything to get a job and don't really care what they actually do (and also because successive govts basically don't give a crap and just wanted a nice and apparently easy way to look like they were Doing Something). The two biggest problem are (1) water getting in through the outer wall and soaking the insulation, eventually wicking across to the inner wall in bad cases. This is partly because of poor materials - although again the industry still uses these - but also because where the exterior wall faces the prevailing weather, CWI should only be used very cautiously. If the exterior wall routinely gets wet, it shouldn't be used (I should add I'm not massively up to date on materials, things like Knauf polystyrene balls are said to be non-wicking, but I've learnt to be pretty sceptical of CWI claims, I was still being offered spun rockwool on an exposed wall in 2017, which was definitely wrong). And (2) because you are basically buying the Emperor's New Clothes. Without a proper infrared heat loss camera before-and-after with some thought given to the heat differential inside and out you have literally no idea whatsoever if the contractors have actually filled the cavity - they are extremely susceptible to patching and cold spots. I offered to pay for a proper CWI job with a long-established contractor using materials of my choice - they were happy with that and quoted but when I told them I wanted to confirm their job afterwards and would expect any cold patches I found to be filled afterwards they ran a mile, they reacted as if I'd just demanded the absurd or incredible. That seems weird to me - what other product is sold like this, it's invisible when installed surely you have to confirm it's actually there? Apparently not. Anyway in the end I decided the whole CWi route is just too dodgy and went for external which has been wonderful.
Nice one 👍 Surprised how cheap your insulation was - I added 175mm onto 100mm into my loft around 10 years back when it was about a fiver a roll - no chance of that these days! Out of curiosity where the patio vent space is do you get any cold bridging and issues with condensation forming when it’s really cold?
it is made from the glass we put out for recycling. If it could be made only during the summer when there is spare solar power then it would be even better for the enviroment
@@utubeape sadly the world doesn’t think in that way, though it would make perfect sense - unless of course it’s scrutinised by those that think there isn’t a problem e.g. stating that renewable lower sources are ‘bad’ because solar panels, turbine blades and batteries aren’t ‘easily’ or ‘can’t’ be recycled 🙄
@@utubeape ROCKWOOL insulation is a rock-based mineral fiber insulation comprised of Basalt rock and Recycled Slag. Basalt is a volcanic rock (abundant in the earth), and slag is a by-product of the steel industry. The minerals are melted and spun into fibers.
@@AliDymock A fine-tooth wood saw works just as well at the correct angle to avoid tearing. If you need lots of different widths is easier to cut through a complete roll before unwrapping the insulation. (Just like cutting a swiss roll)
Few major errors on that job. No vent extensions to reach below insulation. No continuous wind proof layer, having all those gaps makes it pointless. Much better to use an intelligent airtight barrier not plastic sheeting under floor boards on the warm side of the insulation. You should never have plastic sheet continuously touching timber like that as it will encourage mould growth as moisture gets trapped.
Yeh they'd go under the joists, probably attached to the underside then they'd come up through the floor to your radiators. You'll want them to have foam pipe insulation around them as otherwise they'll lose a lot of heat to the cold air under the floor.
Hi. Great video. I am about to buy some underfloor membrane. I just have a question. Does it HAVE to be brethable? One would think that a non-breathable material would be better? what is the purpose of it being breathable?
Just started doing the same at ours, building control needed to be involved cost £515 initial visit to state insulation thickness require for underfloor to be either 200mm rockwool of 100mm celatex. 2nd visit due at end of project in order to sign off, without the certificate they can and do enforce the removal of all the work.
Great video, can I ask about why you left gaps between the pieces of membrane, would this not reduce the performance as wind washing would still occur? I have seen guides online that tape the pieces of membrane together and overlap.
Nice neat job but I would've thought the DPC would seal the floorbards off from the void, and stop any moisture in the floorboards being carried away by the air from the airbricks?
Yup, as Michael Jay said, any moisture in the floorboards can escape upwards. With the insulation below they are now warm so they can be subjected to moisture and it won't condense.
We are in a first floor flat, with a similar floor to yours, and the noise transmission between the flats is incredible with similar insulation in addition to felt over the top of the 4x2 timbers
Not really the right product,silver or non silver backed 4ich boards ect would have been best suited. But the overall finish you achieved is nice and neat.
Certainly a better U-value with PIR but the cost would take a long time to pay back. Getting it air tight with the DPM goes a long way to reduce heat loss by convection I find. If they were 6inch joists then I’d say wool is good enough. At 4inch it’s a toss up.
Really good video and explanation. I find floors can be intermittently damp depending on the time of year. Unless a full CCTV drain survey and soak away check, in my opinion it could be risky insulating a suspended timber floor. Also it is prudent to sleeve the sub floor vents through the cavity just incase something occurs in the future, and restricts sub floor ventilation. An insulated floor because it’s colder, will increase the relative humidity, and could put the timbers at risk of woodworm issues. Might be worth treating the timbers at least for peace of mind👍
Some great points here. You're absolutely right in that adding insulation while all the rage is somewhat of an unknown because there hasn't been a lot of time to study its effect hence why I was really careful with making sure the ventilation isn't interfered with. Of course adding a vapour barrier counters this risk and ensures less vapour is getting through than before even though less vapour can escape. Another good point and I wish I had done some sleeving because the insulation in the cavity walls could drop and block the vents. The good news is I can always do this from the outside of the property later on if I detect any problems. Yeh not sure if these were treated or not actually. 1985 this bit of the house was built, not sure if they treated timbers then. i'll thinking about for the rest of the house.
I'd say that they are all much of a muchness so any thermal mineral wool will do the job. They come in different thicknesses though so make sure you match that to your joist depth
If the crawl space is deep enough to manouvre under the floor, then lift a few floorboards to make an access point, and install fibreglass or Rockwood roll insulation between the floor joists. Staple some garden netting across the underside of the joists to hold the insulation in position. You could use a breather membrane here, but it can be very awkward to] position it and Staple at the same time. Overall cheaper than using rigid insulation but slightly less insulation value. Do not arrest if you are at all claustrophobic.
