Adsibob

Economical way to combine soundproofing and UFH

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Converting a 3 bed very dilapidated 1930s semi into a 4.5 bed modern home. EVERYTHING is being gutted except the joists.

 

Quotes are way over budget, particularly for the underfloor heating. I had specified wet underfloor heating throughout all three floors of the house (ground = 800 sqft, first = 750 sq ft and loft = 450 sqft), with the ground being imbedded into screed and the first and second floors being laid within some high performance extruded polystyrene boards made by Cellecta called XFLO. XFLO is quite expensive, about £26 a square metre, but the reason I had specified them is that they provide good insulation to make sure the heat goes up, are CNC drilled by Cellecta to meet any pipe layout requirements  we specify and also feel quite firm underfoot. The other advantage of the XFLO is that you can lay the finished floor directly onto it. Underneath those XFLO boards, I had specified a 6mm dense rubber matting (which comes as a 10m by 1m rolled product, so pretty easy and quick to lay) to absorb impact sound, and underneath that 18mm tongue and groove ply which is nailed directly onto the joists (whereas the rubber and XFLO are just floating).

 

In between the joists I was going to have mineral wool to mute airborne sound travel, and underneath the joists I was going to have the ceiling attached using resilient bars (with market name "Genie clips") to isolate the ceiling from the joists to further prevent sound transmission.

 

The whole system is to be zoned as 9 zones, including one zone for the 3 towel radiators (which will be the only radiators in the house, one for each bathroom), although I'm going to provide Tado thermostats, one for each of the 8 UFH zones and a Tado smart valve for each of the towel radiators. 

 

One builder has quoted about £25k plus VAT for all of the above, and the other about £28k plus VAT. These quotes don't include the thermostats (I'm providing those). When I have challenged each of them on why this is so expensive (I was expecting about half the cost) they have said different things.  The first builder has said that I could save £2,500 to £3,000 money by losing UFH in the loft and in most of the first floor, and instead having radiators there. The second builder doesn't agree that would save any money and is also trying to respect our reasons for having UFH. Instead he just thinks the system I've specified for the first and second floor is overkill and that I could make two changes which would save about £4k in labour:

 

First, instead of 18mm ply plus 6mm rubber matting plus the XFLO boards (which are about 28mm thick) I should just lay a product sold by theunderfloorheating store calledProWarm ProFloor 22mm pre-routed chipboard. I've looked this up and I see the benefit. Like the XFLO boards, you attach it directly to the joists and it comes routed (though with standard not bespoke routing) and enables you to fix the finished floor directly. It costs roughly the same as the XLFO, but it saves the builder the trouble of having to lay the rubber matting and the ply, so the saving is in the cost of the matting (£6 per sq metre), the ply (about £14 a sq metre) and the labour to fit those two layers.

 

Second, he says that in the bathrooms, I should just lay electric UFH rather than wet. He accepts it's dearer to run, but he says I can have smart timers on it to make sure I only have it on when needed and as there will be wet towel rails in there, I really won't use it that often.

 

I think I'm willing to accept his second point and fir the electric UFH in the bathrooms, but I'm concerned about the disadvantages of the first point, which I see as follows:

 

1) I lose the impact sound protection provided by the  6mm rubber - is this such a big deal given I have an isolated ceiling and the mineral wool between the joists? If so, can anyone think of a way of combining a fairly cheap but effective sound impact layer with the 22mm pre-routed chipboard? It would only ever be my kids running around, so impact sound is not a major issue, but I want some protection.

2) Chipboard is not as durable or as strong as ply. Although both will feel similar at the outset of their lifespan, what will they feel like in 12 years time? I plan to be at the property for 12 years at least, but hopefully longer and I don't like springy floors.

3) no bespoke pipe channels like Cellecta offer with XFLO. But is this overkill? Maybe I don't need bespoke pipe layouts. Builder says that the 22mm pre-routed chipboard just has channels at 200mm pipe centres and that is a standard construction for first and second floors. Although most of the rear of the house is being extended, so it will have insulated cavity walls, and the loft will also be well insulated, the rest of the house has no cavity walls.

 

Keen to hear your thoughts on the above. Thanks for your time!!!

 

 

 

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If your house is properly insulated there will be no real point in having underfloor heating upstairs.  Maybe have a rethink.

 

What is the issue you have with sound transmission?

 

This may be easier as more than one post.

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11 hours ago, Adsibob said:

but the reason I had specified them is that they provide good insulation to make sure the heat goes up,

?

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I think you need to go back to the drawing board, It looks like you are trying to build a sauna, if you insulate it properly and air seal it you will not need heating in the loft, it will be unbearable up there and you will need the windows open. 

 

I have a mezzanine area with no heating apart from what rises naturally and we are wondering how to keep it cool. 

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51 minutes ago, SteamyTea said:

?

Although the rules of thermodynamics say that heat should travel upwards on its own (by conduction to the floor covering and then convection to the air above), everyone in the underfloor heating industry says that you need to insulate underneath the underfloor heating system to prevent wasting heat "leaking" downwards. I guess  the purpose of the insulation underneath is to prevent the heat travelling via conduction to the subfloor and by convection to the void underneath the subfloor. So there has to be some form of insulation I think. Or am i wrong about this?

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20 minutes ago, Russell griffiths said:

I think you need to go back to the drawing board, It looks like you are trying to build a sauna, if you insulate it properly and air seal it you will not need heating in the loft, it will be unbearable up there and you will need the windows open. 

 

I have a mezzanine area with no heating apart from what rises naturally and we are wondering how to keep it cool. 

Thanks for your response. To be clear, the way the house is currently insulated (or rather, not insulated) we only use the central heating 7 or 8 months a year. Although I am going to be installing new double glazing everywhere and although most of the rear of the house and the loft will be properly insulated, the front of the house and the detached side of the house won't have any insulation. Are you saying that even in the middle of winter, you don't need any additional heating in your loft? Also, wouldn't insulation between the floors (as I'm suggesting) prevent the heat from downstairs heating up the loft?

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3 minutes ago, Adsibob said:

rear of the house and the loft will be properly insulated,


to what level? Also if the rest is not insulated it won’t make a lot of difference!!!. You really need to work out your heat load. I have a two story new build and no heating upstairs and rely on heat rising from UFH downstairs.

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15 minutes ago, joe90 said:


to what level? Also if the rest is not insulated it won’t make a lot of difference!!!. You really need to work out your heat load. I have a two story new build and no heating upstairs and rely on heat rising from UFH downstairs.

To the minimum level required by building regs when you build a rear extension and a loft conversion. I'm a layman so I don't know what those minimum levels are, but the point is that the front and side of the house are not being upgraded because of a combination of lack of space and budget, whereas the whole of the ground floor is benefitting from a full width rear extension, and half of the first floor is benefitting from a half width rear extension, and the loft is being converted and insulated all over. I agree that this means the rooms with "old" uninsulated walls will lose much more heat, but due to the layout of the house there won't be many of those rooms and also, those rooms have their own heating zones and so shouldn't impact on the rooms which are benefitting from new walls/new loft insulation. I think comparing my house to a new build is not really an apt comparison in that I'm doing my best to upgrade a 90 year old house that has no cavity walls. There is a limit to what can be achieved without spending a small fortune.

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4 hours ago, Moonshine said:

Use joist caps rather that the rubber matting?

 

https://www.soundstop.co.uk/ZMJCAP50.php

 

Though bear in mind you cant screw through them.

This looks like a very clever way to save on labour and materials and I can immediately see that laying this I can lose the 6mm rubber matting. But if you can't screw through these joist caps, is it fine to just lay a floating floor directly on top. What would that floor structure be? Wouldn't I still need 18mm ply and then some form of underfloor heating board?

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Thermal conduction is to do with temperature differences. Convection is to do with physically moving, in this case, air.

Now a ground floor sitting on the foundation, and then the semi infinite heat sink of the earth, will conduct energy from the UFH to the ground, so that needs lots of insulation. Between floors is a different issue in reality. Convection dominates.

Warm air rises and then gets trapped by the ceiling. This reduces the  ∆T between the air temperature and the UFH system temperature. Between joists is also, generally, an air pocket, so has fairly decent thermal properties.

What is important is reducing unwanted, or uncontrolled, air movement between the house and the exterior. This will, apart from being drafty, cause disproportionate energy losses.

So while the place is stripped bare, make sure that area is airtight, it is easy and cheap to do when nothing, apart from the joists, is in the way.

Consideration must be taken into account for condensation risks, but that is a different issue.

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14 hours ago, Adsibob said:

Converting a 3 bed very dilapidated 1930s semi into a 4.5 bed modern home. EVERYTHING is being gutted except the joists.

 

1 hour ago, Adsibob said:

Although I am going to be installing new double glazing everywhere and although most of the rear of the house and the loft will be properly insulated, the front of the house and the detached side of the house won't have any insulation.

 

If suitable at least check/get cavity wall insulation for all walls not to be 'internalised' by your extensions.

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1 hour ago, A_L said:

 

 

If suitable at least check/get cavity wall insulation for all walls not to be 'internalised' by your extensions.

Unfortunately we've already checked the existing walls of the house and they are solid - no cavity.

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You would be better off taking £10,000 from your ufh budget and spend it on upgrading your insulation, even your loft conversion with current building regs insulation is poor. 

Upgrade it now while the house is a wreck. 

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2 hours ago, Russell griffiths said:

You would be better off taking £10,000 from your ufh budget and spend it on upgrading your insulation, even your loft conversion with current building regs insulation is poor. 

Upgrade it now while the house is a wreck. 


I agree, even some insulation is better than none on your solid walls, foam on plasterboard internally or external wall insulation. Nows  the time to get it done well. Most here double or triple building regs insulation wise. The old adage here is you only buy insulation once, fuel for heating you pay for continuously and it goes up in price regularly.

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6 minutes ago, joe90 said:


I agree, even some insulation is better than none on your solid walls, foam on plasterboard internally or external wall insulation. Nows  the time to get it done well. Most here double or triple building regs insulation wise. The old adage here is you only buy insulation once, fuel for heating you pay for continuously and it goes up in price regularly.

That’s the lesson I have learned on my last 2 renovations.
 

The 1st didn’t have a cavity and so I just assumed I couldn’t do much about it so just threw in loads of heating. 

 

The other I just insulated to BC standards, which I now realise is the bare minimum you should have.

 

I would spend most of that budget you have for heating on insulation and then you’d only need a smaller heating solution. 

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All these suggestions sound very sensible. Thank you.  I will definitely insulate all external walls. Can anyone recommend an insulative plasterboard that won’t cost me more than 50mm in lost depth, but will still give good protection against heat loss?

 

We are also going to try re-render externally, both to conceal the existing pebbledash (which I hate) with something smooth and also to improve insulation, but this is cost-dependent. 

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8 hours ago, Adsibob said:

We are also going to try re-render externally,


Perfect time to EWI (external wall insulation) if it’s within your budget.

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Looking at this objectively and also financially (given I don’t know where you are in the U.K.) then this looks a very expensive solution to a problem you don’t need to have. 
 

UFH in older houses with poor insulation generally doesn’t work well - rate of heat lost vs heat input in solid walls will mean the UFH will struggle to keep up. You say you run the CH now for 7-8 months - UFH won’t fix that unless you fix the source of heat loss. 
 

As others have recommended you need to increase the levels of insulation in the new areas past building regs. New ground floors should be a minimum of 130mm of PIR or 250mm of EPS. Walls should be increased to 150mm full fill cavity or lined with 50mm PIR or PIR backed plasterboard. Attic ceilings should be 150mm of PIR preferably 100mm between and 50mm over rafters. All joints should be taped and you should also ensure any flat ceiling areas in the new build are 400mm fibre insulation.  
 

In terms of existing walls, then consider internal insulation now whilst the walls are bare - 50mm PIR battened back to the existing walls with 25mm infil between will allow you to completely skin the inside of the house with a single layer of insulation with no gaps. The batten layer allows you to have a service void where needed and also fix ordinary plasterboard so is cheaper than using insulated plasterboard. 
 

Without removing the joists or doing a lot of additional work you are not going to remove the noise transmission 100%, and tbh that is something you need to work out if you really need. I would assume the joists are all at 24” or 600mm centres, so first job is to get those beefed up to stop bouncing or the floor acting like a drum. Again, assuming they are 8x2 joists get the the builder to put noggins every 1200mm with 6x2 flush to the surface of the current joists and then D4 glue and screw new 22mm Egger or Caberdeck to the joists. This will stop the floor moving but also leave a void for 50mm of acoustic rockwool insulation above the ceiling that will reduce your sound transmission between floors. 
 

Finally as I said before I would ditch the UFH in the first and second floor and go for designer rads or similar. You can still have zone control using rad valves but you will save massive amounts on the products you’ve specified. Your current Cellecta/Ply sandwich is about £30 or so per square metre excluding the two lots of labour to lay the individual layers, shop around and decent P5 Egger or Caber is £6-7. That £23 pays for over 4 sqm of 50mm PIR for your walls so you are cost neutral before we factor in anything like the costs of the UFH itself which given your builders prices I think is very expensive...!!
 

I would seriously consider back to the drawing board and do a fabric first approach and then look at what you are trying to achieve as I can’t see how some of the products you’re using will give you any benefit in either short or long term. 

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If you IWI then you can also put in a service cavity for pipes and cables.

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PeterW that’s really helpful, 

15 hours ago, PeterW said:

50mm PIR battened back to the existing walls with 25mm infil between will allow you to completely skin the inside of the house with a single layer of insulation with no gaps. The batten layer allows you to have a service void where needed and also fix ordinary plasterboard so is cheaper than using insulated plasterboard.

Sorry for being so dense, but what is 50mm PIR? And will this still allow the walls to breathe? I asked my builder today about installing an insulated plasterboard which is 52.5mm thick to the inside of the external walls and he said he wouldn’t recommend it because the walls needed to be ventilated. We have pebbledash painted white on the outside, that looks pretty old. He said pebbledash is not good for walls, and if I add insulated plasterboard I will make it worse.

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7 hours ago, Adsibob said:

PeterW that’s really helpful, 

Sorry for being so dense, but what is 50mm PIR? And will this still allow the walls to breathe? I asked my builder today about installing an insulated plasterboard which is 52.5mm thick to the inside of the external walls and he said he wouldn’t recommend it because the walls needed to be ventilated. We have pebbledash painted white on the outside, that looks pretty old. He said pebbledash is not good for walls, and if I add insulated plasterboard I will make it worse.


not sure where he is going with that as it is common practice to use either rigid insulation or insulated plasterboard on the inside of solid walls to improve thermal efficiency ! 

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On 17/10/2020 at 09:22, PeterW said:

Your current Cellecta/Ply sandwich is about £30 or so per square metre excluding the two lots of labour to lay the individual layers, shop around and decent P5 Egger or Caber is £6-7.

How durable is a P5 chipboard product going to be vs ply? In ten years’ time, won’t the chipboard soften up slightly and start to be a bit springy compared with an equivalent thickness of ply?

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