Insulated Slab Question

[IanR]

2 hours ago, Shaun McD said:

It will be fixed to the inside of the stud, with joints taped to act as vapor and airtight layer,

 

38 minutes ago, Thorfun said:

i don't recall reading a single self-build on here where they didn't have some form of VCL membrane internally to the insulation. even if that was simple plastic sheeting.

 

I don't have a distinct VCL membrane in my build-up. I have foil-backed plasterboard that restricts moisture entering the wall/roof. Unlike your air-tightness layer, the VCL can have small gaps and breaks, as long as each layer towards the exterior has a higher vapour permeability than the one before.

 

Just for good measure, I also don't have a distinct air tightness membrane. My frame is externally sheathed with T&G Egger DHF board that has a non-curing butyl adhesive in all joints, which is the air-tight layer.

Edited February 22, 2023 by IanR

[Thorfun]

26 minutes ago, Shaun McD said:

 

I would be quite cynical about these things too ha, and they do add the VCL layer to flat ceilings for example. I am sure they will have no issue (just an extra cost) to install the membrane on top of insulation, but they are adamant it is not needed due to their use of the breathable racking board on the outside, hopefully someone on here is more informed and can confirm or deny the validity! 

so no breathable membrane on the outside either? just the 'breathable racking board'? i thought it was pretty standard to use OSB covered in a breathable membrane externally?

 

i guess there are many ways to skin a cat as they say.

[Thorfun]

9 minutes ago, IanR said:

 

 

I don't have a distinct VCL membrane in my build-up. I have foil-backed plasterboard that restricts moisture entering the wall. Unlike your air-tightness layer, the VCL can have small gaps and breaks, as long as each layer towards the exterior has a higher vapour permeability than the one before.

 

Just for good measure, I also don't have a distinct air tightness membrane. My frame is externally sheathed with T&G Egger DHF board that has a non-curing butyl adhesive in all joints. 

every day is a learning day! 🙂

[SteamyTea]

2 minutes ago, Thorfun said:

thought it was pretty standard to use OSB covered in a breathable membrane externally

Isn't that the wind tight layer?

That is usually vapour open in the UK climate.

[IanR]

37 minutes ago, Shaun McD said:

but they are adamant it is not needed due to their use of the breathable racking board on the outside, 

 

That's sounds the same as my external Egger DHF layer. I do have a "breather" membrane on this, trapped under the cladding batons, which protects the sheathing from weather in the short-term, until the cladding and roof finishes are on, and continues to protect in the long term in case any water breeches the rain-screen.

[Shaun McD]

19 minutes ago, IanR said:

 

That's sounds the same as my external Egger DHF layer. I do have a "breather" membrane on this, trapped under the cladding batons, which protects the sheathing from weather in the short-term, until the cladding and roof finishes are on, and continues to protect in the long term in case any water breeches the rain-screen.

 

Yeah sorry I forgot to add the actual weather material wrap on the external side of the "breathable" racking material as standard too

[Thorfun]

1 hour ago, SteamyTea said:

Isn't that the wind tight layer?

That is usually vapour open in the UK climate.

yeah. exactly. a breathable layer on the outside of the TF and the AVCL internally. thought it was pretty standard.

[dpmiller]

@Shaun McD you shouldn't have any issues with Kudos, I'd say they're on a par with MBC based on the quotes, spec, and meetings I had back before we began.

 

/ we ended up going with Leadon's tho as being the best price vs spec option...

[Iceverge]

On 22/02/2023 at 11:13, Shaun McD said:

Yeah TF company would be installing both cellulose and the 70mm PUR/PIR onto studs. Ceilings will also have blown cellulose, so dont think there is any area to cut PUR/PIR.

 

Rockwool, cellulose, hemp, anything is better than Oil based products unsurprisingly. 

 

On 22/02/2023 at 11:13, Shaun McD said:

Yeah TF company would be installing both cellulose and the 70mm PUR/PIR onto studs. Ceilings will also have blown cellulose, so dont think there is any area to cut PUR/PIR. Twin wall system would be nice to have, but have we are very limited with installers in our region, and anyone who is willing to travel has been out of budget.

 

 

Ask you TF company the question about this build up. 225mm timber is an off the shelf item.  Better at damping the temperature swings and much superior for airtightness. You can inspect the cellulose install too and ensure that no slumping has occurred before boarding out. 

 

 

Better Still swap out the OSB for @IanR Egger MDF, you'll get an element of EWI for the studs from the MDF. 

 

On 22/02/2023 at 11:58, Shaun McD said:

Yeah they provide for a test and its in the contract to be under 2.5, but we have a gentleman's agreement that the target is 1.5!

 

LOWER!!!!! it's not rocket science. Head for passive levels. Best money you'll spend! 

23 hours ago, Shaun McD said:

What type of DIY rig are you thinking? Your own blower? 

 

I'm going to do a post on my rig later. 

 

 

 

[Shaun McD]

3 hours ago, Iceverge said:

 

Rockwool, cellulose, hemp, anything is better than Oil based products unsurprisingly. 

 

 

 

Ask you TF company the question about this build up. 225mm timber is an off the shelf item.  Better at damping the temperature swings and much superior for airtightness. You can inspect the cellulose install too and ensure that no slumping has occurred before boarding out. 

 

 

Better Still swap out the OSB for @IanR Egger MDF, you'll get an element of EWI for the studs from the MDF. 

 

 

LOWER!!!!! it's not rocket science. Head for passive levels. Best money you'll spend! 

 

I'm going to do a post on my rig later. 

 

 

 

 

Thank you for this @Iceverge very informative! 

The two TF suppliers who we had down selected too were Kudos (who build per the first wall system) and Long Life Structures (who build per the second wall system). We did discuss with Kudos the option to have them build wall system 2 and other wall systems (TF with external insul, no cavity), and while they where more than happy to do so, it naturally comes at a cost premium to have them produce a one off wall system on their "production line", so we decided that since on paper at least, the end performance result would not be massive, we decided to take the saving and let them do what they do best. 

You have reminded me of something however that was included by LLS but have not discussed yet with Kudos, the 45mm service cavity insulation. I will be flagging that and can self install prior to plasterboarding!

 

Agreed re ACH, 2.5 is a lot higher than we intend to achieve, and again Kudos have offered greater results by different wall systems but we have to draw the line somewhere again on cost. All of these elements are very critical and unfortunately, we are not in the position to opt for the 0.6 ACH guaranteed twin wall systems so will have to do some level of compromise and elbow grease to get what we want! 

[Nickfromwales]

17 hours ago, Shaun McD said:

 

Thank you for this @Iceverge very informative! 

The two TF suppliers who we had down selected too were Kudos (who build per the first wall system) and Long Life Structures (who build per the second wall system). We did discuss with Kudos the option to have them build wall system 2 and other wall systems (TF with external insul, no cavity), and while they where more than happy to do so, it naturally comes at a cost premium to have them produce a one off wall system on their "production line", so we decided that since on paper at least, the end performance result would not be massive, we decided to take the saving and let them do what they do best. 

You have reminded me of something however that was included by LLS but have not discussed yet with Kudos, the 45mm service cavity insulation. I will be flagging that and can self install prior to plasterboarding!

 

Agreed re ACH, 2.5 is a lot higher than we intend to achieve, and again Kudos have offered greater results by different wall systems but we have to draw the line somewhere again on cost. All of these elements are very critical and unfortunately, we are not in the position to opt for the 0.6 ACH guaranteed twin wall systems so will have to do some level of compromise and elbow grease to get what we want! 

This early on in the game you can discuss here and find where this frame is going to leak, and make a plan to mitigate against it at relatively low cost impact.

Getting the ACH down to 1.0 or less, will be a very fruitful endeavour, as the closer to 3.0 you get, the worse the effectiveness of the HR element of the MVHR.

Get involved, find the weak points of your chosen frame, and get your hands ( and elbows ) dirty!!  

[IanR]

19 hours ago, Shaun McD said:

Agreed re ACH, 2.5 is a lot higher than we intend to achieve.

 

2.5 ACH seems an odd target to me. Depending on building proportions, 2.5 ACH is in the region of 3m³/m².h @50 PA infiltration rate, which is the threshold at which whole house mechanical ventilation is deemed required as there is insufficient natural ventilation for reasonable internal air quality.

 

At that target, you have to install mechanical ventilation, but receive no benefit and therefore no pay-back for the cost on the install. There's a lot to save from better air-tightness, but if you are to go better than 3m³/m².h @50 PA, then shoot for 1m³/m².h @50 PA (approx. 0.6ACH), in order to get a return on the MVHR investment.

Edited February 24, 2023 by IanR

[Shaun McD]

3 hours ago, Nickfromwales said:

This early on in the game you can discuss here and find where this frame is going to leak, and make a plan to mitigate against it at relatively low cost impact.

Getting the ACH down to 1.0 or less, will be a very fruitful endeavour, as the closer to 3.0 you get, the worse the effectiveness of the HR element of the MVHR.

Get involved, find the weak points of your chosen frame, and get your hands ( and elbows ) dirty!!  

 

Solid idea, I will get a thread going in the TF section around experiences and best practices! 

 

1 hour ago, IanR said:

 

2.5 ACH seems an odd target to me. Depending on building proportions, 2.5 ACH is in the region of 3m³/m².h @50 PA infiltration rate, which is the threshold at which whole house mechanical ventilation is deemed required as there is insufficient natural ventilation for reasonable internal air quality.

 

At that target, you have to install mechanical ventilation, but receive no benefit and therefore no pay-back for the cost on the install. There's a lot to save from better air-tightness, but if you are to go better than 3m³/m².h @50 PA, then shoot for 1m³/m².h @50 PA (approx. 0.6ACH), in order to get a return on the MVHR investment.

 

Agreed, a bit of an odd target, and we are talking still around what we want our target to be and the best way to achieve it, i.e. via Kudos or DIY. 

In fairness to Kudos, as essentially a sub contractor, with no ownership on glazing, foundations, internal rising wall junctions etc. I have some understanding why they would like to air on the side of caution (pardon the pun) and not commit to a result without owning more trades. They have already prompted me to look at the "blowerproof" paint, sorry cannot remember the brand, and to think about applying it on internal rising walls

[Nickfromwales]

42 minutes ago, Shaun McD said:

I have some understanding why they would like to air on the side of caution (pardon the pun) and not commit to a result without owning more trades.

It's because it would be a suicide mission, as guaranteed the follow on trades will decimate all of their efforts made, to the point up to where they disengaged.

[TerryE]

On 22/02/2023 at 08:39, jack said:

Again, a large number of people on BuildHub have insulated raft foundations, and the issues you've raised either don't exist or are easily dealt with.

I am one of them.  I endorse pretty much everything that  @jack and @Nickfromwales have said.  IMO, having this type of warm slab was up there amongst the best design choices that I made.  The only embedded service in-slab is the PexAlPex UFH loops that are designed to be embedded in concrete.  Everything else is run through the service and floor voids.  We did add four piping / cabling ducts under slab and rising in our equipment area.  We used 110mm drainage pipe for this because we needed so much anyway.  

 

One hint though if you do use this trick: use a slow bend or 2×45° to turn through the slab as this makes pulling through a lot easier.

 

Another advantage of a single raft pour is that the FFL is flat across the entire ground floor to within a few mm.  You don't the between room bumps that can occur if the UFH teams pour a self leveling screed per room.

[Shaun McD]

14 minutes ago, TerryE said:

I am one of them.  I endorse pretty much everything that  @jack and @Nickfromwales have said.  IMO, having this type of warm slab was up there amongst the best design choices that I made.  The only embedded service in-slab is the PexAlPex UFH loops that are designed to be embedded in concrete.  Everything else is run through the service and floor voids.  We did add four piping / cabling ducts under slab and rising in our equipment area.  We used 110mm drainage pipe for this because we needed so much anyway.  

 

One hint though if you do use this trick: use a slow bend or 2×45° to turn through the slab as this makes pulling through a lot easier.

 

Another advantage of a single raft pour is that the FFL is flat across the entire ground floor to within a few mm.  You don't the between room bumps that can occur if the UFH teams pour a self leveling screed per room.

 

Thanks @TerryE we are hoping we can find a local installer and go this route! Re services in slab, for ground floor plumbing, i.e. toilet feeds, dhw and cold to sinks, showers, basins etc. are you saying that all of these came down from first floor ceiling instead of up from slab?

[Nickfromwales]

48 minutes ago, Shaun McD said:

 

Thanks @TerryE we are hoping we can find a local installer and go this route! Re services in slab, for ground floor plumbing, i.e. toilet feeds, dhw and cold to sinks, showers, basins etc. are you saying that all of these came down from first floor ceiling instead of up from slab?

I do that for most clients, but occasionally, if the topology lends itself, I will go through the slab ( insulation layer ). Eg on my current one at Gravenhill I am doing this with the kitchen sink so I can avoid having to install a hot recirculation system.

I just needs a lot of thought and coordination, and sometimes it's impractical as other trades will be screaming at you to get a wiggle on.

[Shaun McD]

6 minutes ago, Nickfromwales said:

I do that for most clients, but occasionally, if the topology lends itself, I will go through the slab ( insulation layer ). Eg on my current one at Gravenhill I am doing this with the kitchen sink so I can avoid having to install a hot recirculation system.

I just needs a lot of thought and coordination, and sometimes it's impractical as other trades will be screaming at you to get a wiggle on.

 

Thanks @Nickfromwales I was not aware it was common to drop these services, so good to know. I just seen a youtube video the other day about dhw recirculation systems, and that they are worth doing ha! Would you avoid from a installer POV, or is there no real merit in the idea?

[Nickfromwales]

39 minutes ago, Shaun McD said:

 

Thanks @Nickfromwales I was not aware it was common to drop these services, so good to know. I just seen a youtube video the other day about dhw recirculation systems, and that they are worth doing ha! Would you avoid from a installer POV, or is there no real merit in the idea?

I install HRC's on 95% of my turnkey M&E installs, so yup. You just need to insulate the hot and the hot return VERY well.

Lots on here about how to control them, with my favourite being via PIR / occupancy sensors in each bathroom etc.

[TerryE]

@Shaun McD, Using the 1st floor void for distribution, then drop or rising the services vertically through the service void is a very common approach adopted by many here.  We did all of our own plumbing, largely under the inspiration and remote guidance of @Nickfromwales, a.k.a my hero 🤩.   This saved us a load of money, and honestly we ended up with a far superior installation than if we've used our builder's preferred plumber.  It was all relatively easy stuff.  

 

There are loads of threads and blog entries from members on their individual implementations, so it is well worth getting a glass of vino, and doing a few hours browsing of these for hints and examples.  This will get you started and save you loads of grief. 

 

I did the central plumbing in copper.  I had done some copper / end-feed work before (about 25 years previously), but you just need to watch a few YouTube videos and have a few practice attempts.  I did very little soldering in-place but instead used the valves, etc. plus the odd compression connector too break up copper-work into sections that I could bench solder/assemble, and since these sub-units ended in compression tails, I could add a few temporary end stops to allow me to pressure test the sub-units before assembly.   The basic topology was hub and spoke using brass manifolds and Hep2O 1-1 to the whitegoods, etc.  Jan and I split the Hep2O 50:50, and she'd never done any plumbing before, but soon became proficient.  

 

Have a browse of content here.  Brilliant solution. 🙂

 

[Iceverge]

30 minutes ago, TerryE said:

We did all of our own plumbing, largely under the inspiration and remote guidance of @Nickfromwales, a.k.a my hero 🤩.   This saved us a load of money, and honestly we ended up with a far superior installation than if we've used our builder's preferred plumber.  It was all relatively easy stuff.

 

I did both. ( apart from the save money bit!) 

 

I pulled out the plumbers underperforming compression fit attempt after 6 months and redid it all in Hep2O myself with a radial layout.  

 

25mm MDPE to the stopcock. 

22mm Hep2O to the control block splitting to 22mm for the UVC and cold manifold. 

 

15mm for all cold feeds except the basin and toilets in 10mm. 

 

22mm manifold rising above the UVC to preheat the hot water via convection. 

15mm pipe to the Showers/Baths and Utility 

10mm pipe to the basins and kitchen tap.

 

Kitchen tap should be 15mm really but a run of 13m (woops UVC in wrong location!) meant to have quick hot water delivery at the expense of less flow (6l/sec after 8-9 secs) I used 10mm. The plumber had left us with 10l/s after 35-45 secs which was infuriating. 

 

 

 

I have since done my parents heating and DHW with an oil boiler, solid fuel Rayburn and thermal store. 

 

 

[Shaun McD]

On 25/02/2023 at 12:00, TerryE said:

@Shaun McD, Using the 1st floor void for distribution, then drop or rising the services vertically through the service void is a very common approach adopted by many here.  We did all of our own plumbing, largely under the inspiration and remote guidance of @Nickfromwales, a.k.a my hero 🤩.   This saved us a load of money, and honestly we ended up with a far superior installation than if we've used our builder's preferred plumber.  It was all relatively easy stuff.  

 

There are loads of threads and blog entries from members on their individual implementations, so it is well worth getting a glass of vino, and doing a few hours browsing of these for hints and examples.  This will get you started and save you loads of grief. 

 

I did the central plumbing in copper.  I had done some copper / end-feed work before (about 25 years previously), but you just need to watch a few YouTube videos and have a few practice attempts.  I did very little soldering in-place but instead used the valves, etc. plus the odd compression connector too break up copper-work into sections that I could bench solder/assemble, and since these sub-units ended in compression tails, I could add a few temporary end stops to allow me to pressure test the sub-units before assembly.   The basic topology was hub and spoke using brass manifolds and Hep2O 1-1 to the whitegoods, etc.  Jan and I split the Hep2O 50:50, and she'd never done any plumbing before, but soon became proficient.  

 

Have a browse of content here.  Brilliant solution. 🙂

 

 

On 25/02/2023 at 12:43, Iceverge said:

 

I did both. ( apart from the save money bit!) 

 

I pulled out the plumbers underperforming compression fit attempt after 6 months and redid it all in Hep2O myself with a radial layout.  

 

25mm MDPE to the stopcock. 

22mm Hep2O to the control block splitting to 22mm for the UVC and cold manifold. 

 

15mm for all cold feeds except the basin and toilets in 10mm. 

 

22mm manifold rising above the UVC to preheat the hot water via convection. 

15mm pipe to the Showers/Baths and Utility 

10mm pipe to the basins and kitchen tap.

 

Kitchen tap should be 15mm really but a run of 13m (woops UVC in wrong location!) meant to have quick hot water delivery at the expense of less flow (6l/sec after 8-9 secs) I used 10mm. The plumber had left us with 10l/s after 35-45 secs which was infuriating. 

 

 

 

I have since done my parents heating and DHW with an oil boiler, solid fuel Rayburn and thermal store. 

 

 

 

I never even thought of doing my own plumbing, was the one I would be most scared off ha! The house will be pretty simple plumbing wise, but over longer distances from the single story layout. I also have a specific request from the better half to ensure our ensuite shower has LOADS of water pressure, so I need to figure out how to go about that. 

We will have a service void in the ceiling (which I assumed would be 50mm but I have seen some people put their MHRV pipes in here, so this would need to be 100mm in that case), but is that where the pipes would be? Or would they be on the joist? On the joist would need to be taken through air tightness layer, where as in service would not. 

 

[Thorfun]

1 hour ago, Shaun McD said:

 

 

I never even thought of doing my own plumbing, was the one I would be most scared off ha! The house will be pretty simple plumbing wise, but over longer distances from the single story layout. I also have a specific request from the better half to ensure our ensuite shower has LOADS of water pressure, so I need to figure out how to go about that. 

We will have a service void in the ceiling (which I assumed would be 50mm but I have seen some people put their MHRV pipes in here, so this would need to be 100mm in that case), but is that where the pipes would be? Or would they be on the joist? On the joist would need to be taken through air tightness layer, where as in service would not. 

 

if you have a warm roof (or warm loft) with the insulation between the rafters then your loft space will be within the heated and airtight envelope which will allow you to run services in the loft space easily and without worrying about heat loss in to an uninsulated void or penetrating the airtight layer.

[JackofAll]

On 24/02/2023 at 14:42, TerryE said:

I am one of them.  I endorse pretty much everything that  @jack and @Nickfromwales have said.  IMO, having this type of warm slab was up there amongst the best design choices that I made.  The only embedded service in-slab is the PexAlPex UFH loops that are designed to be embedded in concrete.  Everything else is run through the service and floor voids.  We did add four piping / cabling ducts under slab and rising in our equipment area.  We used 110mm drainage pipe for this because we needed so much anyway.  

 

One hint though if you do use this trick: use a slow bend or 2×45° to turn through the slab as this makes pulling through a lot easier.

 

Another advantage of a single raft pour is that the FFL is flat across the entire ground floor to within a few mm.  You don't the between room bumps that can occur if the UFH teams pour a self leveling screed per room.

@TerryE @Nickfromwales not sure if how they lay the pipes in this clip is right but it sure does look easy. 

 

[jack]

1 hour ago, JackofAll said:

@TerryE @Nickfromwales not sure if how they lay the pipes in this clip is right but it sure does look easy. 

 

As far as I can tell, most people on BuildHub who have an insulated raft have their UFH pipes zip-tied to the reinforcement mesh as shown in this video. It's certainly how mine was done.