MaryM

Hello again, more trouble!!!

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Hi everyone, I've written a lot about my garage job under the 'Hello & Panic' thread and got a lot of helpful advice

 

now have another problem and no idea which subject to post under so here I am again

 

not long ago I decided to go the full conversion compliance route but after a lot of research the costs were beyond my budget

 

so I've had to change tack and put the space back to 'garage' status, negotiating with my builder to take out the stud dividing wall and radiator, the jury is still out on whether the window is worth keeping as I haven't yet got a quote for Regularisation from building control, it's with them for consideration

 

a lot of insulation has been put on the external single skin brick wall using stud timer and a Knauf product, not sure which one, it's proposed to put plasterboard over that to form the inner garage wall

 

I was advised to look at the Knauf site and was worried that they recommend a barrier between the insulation and brick, and a vapour barrier between the stud timber and insulation, I have neither of these, photos attached

 

because I've had to lose the radiator the garage will still be very cold and I'm worried about condensation inside the wall, as you can see there's a lot of electrics sitting on the insulation and even with my minimal knowledge, electricity & water don't mix!

 

there is no damp proofing in the floor, there's a conventional damp course in the brick outer & block party walls, there's a suspended timber floor over a concrete slab that lies directly on subsoil, no obvious damp barrier so likely the stud timber is screwed directly to the timber floor surface with no damp barrier

 

my builder proposed cutting off the lower bit of the stud and putting a damp proof membrane between it and the suspended floor, but I've been told that putting a damp proof membrane on top of the suspended floor would also cause a condensation risk under it unless the space is ventilated, which would be very expensive, another photo attached

 

what do you all think about these 2 issues?  

 

is the wall treatment safe in electrical terms and is it worth keeping at all if it encourages condensation & damp?

 

 

utility_external_wall.JPG

switches.JPG

incomplete_electrics.JPG

stud_timber_-_damp_course.JPG

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sorry, it's a barrier between stud timber & plasterboard, not insulation, Knauf diagram attached, I don't seem to have the blue bit or the black bit

Knauf diagram.jpg

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@MaryM sorry to hear that you've not been able to get the situation properly resolved.

 

Unfortunately, I would say the two membranes - certainly the one between insulation and plasterboard - are fairly crucial. The water/electricity issue is a concern, but actually not the biggest one (condensation will most likely form within the insulation towards the outside wall, so a bit away from the socket backboxes).

 

The bigger problem is water/timber. The condensation will get into the wood and quite quickly start it rotting (especially if it's untreated timber - hard to tell from the photos but looks like it). You may also get mould growth within the wall construction which will eventually migrate into the room side of the plasterboard.

 

Perhaps, if the space isn't heated and you're not doing much wet stuff in there, you may get away with it for a while. The major condensation risk is with warm air (which holds a lot of water) - if the air temperature in the room / in the wall isn't all that different it may be that there's not much moisture there to condense. However I'd be concerned about relying on that.

 

Similarly, if you had a reliable continuous membrane on the inside edge you might get away without the one between wall and insulation. Although in theory moisture can migrate in through a single skin wall (I assume that's what you have) in practice my understanding is it tends to ebb and flow with the weather and so you don't get the same risk of large volumes of condensation building up over time. Again what you have is a concern, but might survive - given it will now be hard to fix you could ask Knauf or one of the other suppliers to do a condensation risk analysis and see what they say. That said even without a full membrane most of the suppliers specify at least damp proof strips between timber and wall (and treated timber) to minimise risk of moisture being absorbed directly out of the masonry.

 

I would also want to see vertical damp proof strips between the end stud and brickwork in your last photo.

 

When I stripped apart the (awful) garage conversion we inherited, I found almost the same as you have (they had put a membrane on the outer edge but none on the inside) and the mould & rot that had developed over about 6 years was pretty significant.

 

My hunch from your description is the floor may be less problematic.

 

If it is a suspended timber floor with a void below then presumably that void is ventilated and the joists for the floor are above the damp proof course in the masonry. In that case the concrete below is expected to be damp, but it doesn't matter. And if there is no insulation in the floor then there's limited condensation risk down there and you should be OK to put a membrane on the floor if required (e.g. for laminate/timber flooring) or leave it as-is if the floor covering is not moisture sensitive. There would ideally be a bit of damp proof below the stud walls, but it's probably not the end of the world if that's been missed. Houses across the country have suspended timber floors with wooden furniture, membranes and laminate floor, etc, sat on them and they don't have problems.

 

If the subfloor is not ventilated then it should be relatively cheap to get that resolved, either with a couple of airbricks or by core drilling for a couple of circular ventilation grilles.

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To be honest, in my opinion regardless of whether the work required building regulations approval it looks like fairly poor work in particular re the detailing of insulation/damp-proofing which I can't having been suitable in any circumstances and I would think the builder ought to be on the hook for putting that right. I hope you're able to get it resolved.

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Is all the wiring in a safe zone, not usual to have cables crossing a wall (though it can be done with the correct mechanical damage protection).

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you are such kind, knowledgeable folk on here!

 

@andyscotland  I've been in touch with Knauf technical this morning who confirm exactly what you say about membranes, they say "a vapour control layer internally and a plasterboard over the face a foil backed plasterboard with taped and sealed joints can be used in place of a vapour control layer."

 

I seem to have got plain old plasterboard, no foil either side, just says 'British Gypsum' and certainly no vertical damp strips anywhere I can see, I'm familiar with tanalised timber from my gardening exploits and the stud timber doesn't look like that

 

the top of the floor level is only about 75mm above the original concrete slab, looks like 3" in old money, I guess it's been done so there is still a sufficient step-down into the garage, I believe the current BR requirement is 100mm and I've still got that, and the chipboard extends right to the edges all round, if there is any ventilation it's hard to see where it could be, at the front there's just a continuous wood strip from the base of the chipboard to the top of the original concrete slab

 

the joists are below the masonry DPC by about 75mm, if you look at the last photo which is where the single-skin brick outside wall meets the brick pier at the front of the garage, the mucky black layer is the DPC so it's a brick and a bit above the top of the flooring chipboard

 

does that make a difference to your advice?  I'm going to go off now and read about airbricks, something new every day!

 

@SteamyTea  sorry I don;t know what is a 'safe zone'?  Knauf have commented that " from the picture it could be difficult to line the sockets when the plasterboard is fitted."

I don't know what that means either ...

 

 

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3 hours ago, MaryM said:

Hi everyone, I've written a lot about my garage job under the 'Hello & Panic' thread and got a lot of helpful advice

 

now have another problem and no idea which subject to post under so here I am again

 

not long ago I decided to go the full conversion compliance route but after a lot of research the costs were beyond my budget

 

so I've had to change tack and put the space back to 'garage' status, negotiating with my builder to take out the stud dividing wall and radiator, the jury is still out on whether the window is worth keeping as I haven't yet got a quote for Regularisation from building control, it's with them for consideration

 

a lot of insulation has been put on the external single skin brick wall using stud timer and a Knauf product, not sure which one, it's proposed to put plasterboard over that to form the inner garage wall

 

I was advised to look at the Knauf site and was worried that they recommend a barrier between the insulation and brick, and a vapour barrier between the stud timber and insulation, I have neither of these, photos attached

 

because I've had to lose the radiator the garage will still be very cold and I'm worried about condensation inside the wall, as you can see there's a lot of electrics sitting on the insulation and even with my minimal knowledge, electricity & water don't mix!

 

there is no damp proofing in the floor, there's a conventional damp course in the brick outer & block party walls, there's a suspended timber floor over a concrete slab that lies directly on subsoil, no obvious damp barrier so likely the stud timber is screwed directly to the timber floor surface with no damp barrier

 

my builder proposed cutting off the lower bit of the stud and putting a damp proof membrane between it and the suspended floor, but I've been told that putting a damp proof membrane on top of the suspended floor would also cause a condensation risk under it unless the space is ventilated, which would be very expensive, another photo attached

 

what do you all think about these 2 issues?  

 

is the wall treatment safe in electrical terms and is it worth keeping at all if it encourages condensation & damp?

 

 

utility_external_wall.JPG

switches.JPG

incomplete_electrics.JPG

stud_timber_-_damp_course.JPG

Sorry to be the barer of bad news 

While the barrier between the PB is important the barrier between the brick and stud is crucial Without it damp will strike 

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17 minutes ago, MaryM said:

you are such kind, knowledgeable folk on here!

 

@andyscotland  I've been in touch with Knauf technical this morning who confirm exactly what you say about membranes, they say "a vapour control layer internally and a plasterboard over the face a foil backed plasterboard with taped and sealed joints can be used in place of a vapour control layer."

 

I seem to have got plain old plasterboard, no foil either side, just says 'British Gypsum' and certainly no vertical damp strips anywhere I can see,

 

To be honest even with foil backed plasterboard the number of electrical penetrations would be an issue - internal air will go through/round the socket holes and switches and then out through the metal backbox into the wall. You can get special backboxes that are designed to continue the vapour barrier, but they are pricey. Normally you would put the vapour barrier over the stud and then fit sockets / cabling. Ideally that would be done with some battens to create a "service void" - a narrow gap between membrane and plasterboard - for the backboxes and cables, the cables can then be fixed to the service void battens rather than through the membrane. You can do it without the service void but it means the membrane will have to curve behind them which increases the risk of tears and splits.

 

17 minutes ago, MaryM said:

I'm familiar with tanalised timber from my gardening exploits and the stud timber doesn't look like that

 

Some treated construction timber isn't as visibly brown/green as tanalised gardening timber, but it will usually have printed markings on the timber to identify it as treated.

 

17 minutes ago, MaryM said:

the top of the floor level is only about 75mm above the original concrete slab, looks like 3" in old money, I guess it's been done so there is still a sufficient step-down into the garage, I believe the current BR requirement is 100mm and I've still got that, and the chipboard extends right to the edges all round, if there is any ventilation it's hard to see where it could be, at the front there's just a continuous wood strip from the base of the chipboard to the top of the original concrete slab

 

the joists are below the masonry DPC by about 75mm, if you look at the last photo which is where the single-skin brick outside wall meets the brick pier at the front of the garage, the mucky black layer is the DPC so it's a brick and a bit above the top of the flooring chipboard

 

does that make a difference to your advice?  I'm going to go off now and read about airbricks, something new every day!


Ah - it sounds like what you have is a concrete base with joists resting directly on it and then the chipboard on that? The timbers being primarily just to have something to fix the chipboard to, and to bring the level up as you say.

 

I wouldn't describe that as a suspended floor (though I can't at the moment think of what I would call it!). Most people take suspended floor to mean having joists that hang from the wall and span the room from side to side, with a gap below (basically identical to e.g. a ceiling/first floor, just nearer the ground and with no plasterboard on the bottom, if that makes sense?).

 

Unfortunately that does change the advice. There should be a damp proof membrane between the concrete and the timber, which should continue up the sides to join in with the DPC in the walls. If not then the current timber/chipboard is relying on ventilation to the room above to keep it dry. It will, unfortunately, be challenging to ventilate it from below (airbricks won't be suitable for that job). Putting a membrane over the top will seal the moisture in and cause it to rot. You could (and should) however have strips of DPC between the studs and the chipboard to stop moisture travelling up into the wall. You then might be able to find a floorcovering that will cope with sitting on slightly damp chipboard and still let the moisture through to the room, but it's not going to be ideal.

 

17 minutes ago, MaryM said:

@SteamyTea  sorry I don;t know what is a 'safe zone'?  Knauf have commented that " from the picture it could be difficult to line the sockets when the plasterboard is fitted."

I don't know what that means either ...

 

That's a good spot by @SteamyTea I didn't notice that at first but agree that from the photos it looks unlikely that the cables are in permitted routes. I think Knauf's comment is as mine above that you would need to do something to make those sockets and the gaps around/between them airtight if using foil plasterboard, otherwise you just have big holes in your vapour control.

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ok, lots more helpful stuff here!

 

@andyscotland correct about concrete floor with joists resting directly on it then chipboard on top, prev owners used the space for their hobby, storage of colossal collection of vinyl records, just stuck some cheap carpet tiles on top of an amateur job although they knew enough to leave the 100mm 'garage' step down from the house

 

I called it 'suspended' as I don;t know how else to describe it either an someone else said that

 

I told you all a long time ago I don;t speak 'builder', I can tell you what size knitting needles to use for 4-ply wool or how much butter to put in a 3-egg Victoria sponge and that's my best offer!

 

however your changed advice makes perfect sense even to me, insulating the garage floor has been relegated to a lost cause and I'd reduced my floor covering expectations from Karndean to garage flooring tiles or roll-out mat

 

thanks to you and @SteamyTea for guidance on the electrics, I'm surprised because the sparky is registered NICEIC, has done lots for me including fuse boards, is very meticulous in certification so I'd expected his work, at least, to be reliable

 

I'm waiting for confirmation on the exact Knauf product used, so far my builder said 'Knauf Insulations Batts 100mm thickness' which I don't think identifies the product with precision?

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1 minute ago, MaryM said:

is very meticulous in certification

Called 'marking your own homework'.

It may well be alright, hard to tell from the pictures, just seemed at first glance and bit close to the surface.

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5 minutes ago, SteamyTea said:

Called 'marking your own homework'.

It may well be alright, hard to tell from the pictures, just seemed at first glance and bit close to the surface.

how close to the surface is it meant to be?  sorry the pictures are not very good and I'm not sure which bits are relevant to pro's like you

 

the plasterboard is attached directly to the stud timber and is 12.5mm thick, the wires run through holes centred 35mm from the surface of the stud, so I guess the wiring is 47.5mm under the surface?  the metal boxes are attached to the stud surface so the wires going in & out of those are further forward, if that makes sense?

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another question:  builder now says insulation is Knauf Dritherm Cavity Slab 37 Standard 100mm 455x1220mm

 

it isn't obvious to me why anyone would use a material designed for brick/block cavity walls in a stud installation, but then what do I know?

 

@andyscotlandwould using this product mean no vapour barriers were needed?  will I ever make sense of this?

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this is the stuff I have got, is it possible to ID by looking at it?  

sample_insulation.JPG

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38 minutes ago, MaryM said:

another question:  builder now says insulation is Knauf Dritherm Cavity Slab 37 Standard 100mm 455x1220mm

 

it isn't obvious to me why anyone would use a material designed for brick/block cavity walls in a stud installation, but then what do I know?

 

@andyscotlandwould using this product mean no vapour barriers were needed?  will I ever make sense of this?

 

There's no particular reason not to have used that - mineral wool is essentially mineral wool. you get it marketed in all sorts of "types" but broadly speaking that's mostly about the size/shape/format of the product that is easiest to install in a particular application e.g. cavity wall slabs are usually sized to fit between standard masonry ties, timber frame slabs and rolls the right width for standard stud thicknesses and spacing, loft rolls for rafter spacing etc. But doesn't mean you have to use a cavity slab in a cavity/loft roll in a loft/etc...

 

The Dritherm he's used does have a water repellent additive so maybe he picked it deliberately for that. Unfortunately it's not going to help : if anything if the repellent works it will just drive it into the timber where it will do most damage. It won't prevent the condensation forming, as it has a high vapour permeability (it lets wet air through happily, the repellent only works on liquid water). In fact you'd almost be better with a water-attracting insulation like natural wool, which tends to suck water in and absorb it (to a point, not recommending using it in your construction). 

 

 

Or he may just have picked it because he had some / it was easiest or cheapest to source / it suited the stud spacings he wanted to use.

 

Either way unfortunately no, it won't avoid you needing proper damp/vapour detailing in the wall.

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Also from a quick look if you have only got 100mm and it's a single skin standard blockwork wall that's going to give a u-value around 0.37 - quite a lot more than you'd have needed to achieve if you'd gone for building regs, even on an extension (I think 0.28 in England though I'm not certain). Still better than an old fashioned house with modern cavity wall insulation so probably still worth having if you can sort the moisture issues.

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5 hours ago, MaryM said:

how close to the surface is it meant to be

50mm, but I guess that 47.5mm is 50mm.

 

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2 hours ago, andyscotland said:

The Dritherm he's used does have a water repellent additive so maybe he picked it deliberately for that. Unfortunately it's not going to help : if anything if the repellent works it will just drive it into the timber where it will do most damage. It won't prevent the condensation forming, as it has a high vapour permeability (it lets wet air through happily, the repellent only works on liquid water). In fact you'd almost be better with a water-attracting insulation like natural wool, which tends to suck water in and absorb it (to a point, not recommending using it in your construction). 

 

Or he may just have picked it because he had some / it was easiest or cheapest to source / it suited the stud spacings he wanted to use.

 

Either way unfortunately no, it won't avoid you needing proper damp/vapour detailing in the wall.

 

@andyscotland  it wasn't because he had some, it was ordered from Travis Perkins for me and it doesn't fit the stud spacings, it's 455 wide and the stud is 300 apart, no idea about comparative price

 

the diagram on the Knauf site for installing cavity slabs doesn't show any vapour barriers, just brick/cavity slab/block, would that be because it's ventilated?  air bricks again?  that would make sense to me with your comments above, because the stud/brick cavity in the garage isn't ventilated at all, flat roof up top (that's also been stuffed full of insulation) and no air bricks, well I suppose you wouldn't in a single brick wall, would you?  whereas the house has them on the brick/block cavity side wall

 

Edited by MaryM

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54 minutes ago, MaryM said:

 

@andyscotland  it wasn't because he had some, it was ordered from Travis Perkins for me and it doesn't fit the stud spacings, it's 455 wide and the stud is 300 apart, no idea about comparative price

 

would the qualities of the cavity slab work in a cavity because it's ventilated?  air bricks again?  that would make sense to me with your comments above, because the stud/brick cavity in the garage isn't ventilated at all, flat roof up top (that's also been stuffed full of insulation) and no air bricks, well I suppose you wouldn't in a single brick wall, would you?  whereas the house has them on the brick/block cavity side wall

 

 

The water repellent properties work in a cavity in a masonry wall because the masonry doesn't care about getting damp, and any water that does get in can run down the cavity and out the bottom. Some cavities are also ventilated (with very small vents - airbricks are usually used below floor level to ventilate right through the wall to the underfloor void, rather than to ventilate a cavity wall cavity). The water repellent additive is just to minimise liquid water that penetrates through/condenses on the outside skin being able to transfer through the insulation to the inner skin.

 

Insulated stud internal linings as you have are often not ventilated, although sometimes set slightly off the wall to give a slight air gap. So long as the membranes are right that's ok.

 

How has the flat roof been insulated - was it insulated already / what type of insulation and where is it / has he put a new roof covering on? There can be similar condensation/rot risks with incorrectly detailed roof insulation upgrades...

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On 08/11/2019 at 13:22, andyscotland said:

To be honest, in my opinion regardless of whether the work required building regulations approval it looks like fairly poor work in particular re the detailing of insulation/damp-proofing which I can't having been suitable in any circumstances and I would think the builder ought to be on the hook for putting that right. I hope you're able to get it resolved.

@andyscotland  my builder is now demanding I pay him for the non-compliant work he's done and for the insulation, I've confirmed there are no vapour barriers at all anywhere.  

 

you expressed the thought the builder 'ought to be on the hook for putting that right', any ideas anyone on how to do that?  I've told him I want my garage made legal again but all he does is ask for money, today I got a demand for another few thousand 'I've got to pay' he says, and it doesn't even add up

 

I'm at the end of my rope, I just want him off my back but I don't know how, I'd even pay someone else to put his work right if he'd stop coming after me for money but I can't afford to pay twice

doesn't add up.JPG

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On 08/11/2019 at 14:45, nod said:

Sorry to be the barer of bad news 

While the barrier between the PB is important the barrier between the brick and stud is crucial Without it damp will strike 

@nod  he wants me to pay for the work he's done (as in the photo) how can the barrier between the brick & stud be corrected without takingi it all out?  so i have to pay him for doing it wrong, pay him again to take it out and pay a third time to put it back right?  no can do!

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Unfortunately it can’t 

It’s his error and if you haven’t paid him His problem 

He either didn’t care or didn’t know 

If you are using Building control 

They would have wanted to inspect prior to plaster boarding 

and would have definitely flagged this issue 

 

You need to be firm on this and tell him Not only will you not be paying  the money owed You will bill him for any extra cost rectifying this bad workmanship 

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thank you @nod I'm sure you're right

 

I have paid him some money and he's trying to intimidate me into paying more, I am trying to be firm but it's hard when I don't know what I'm talking about

I have done my best by reporting the error to Building Control as soon as I found out, stopping the work and trying to get him to put it right but he doesn't want to know about anything until I have paid more money

 

then he can't even send me numbers that add up, and that's something I do know about!

 

I've been up half the night again sick with worry, if I could just get this over with I'd be happy to pay someone else to put it right

 

this is what his website says, you'd believe from that he did know, he did the design, and he specified the works, now he's trying to blame me for not applying to BC181785597_abwprojectmanagement.thumb.JPG.2b2fce539fc0f4613050a7b5ba4fa072.JPG

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I’m sorry to hear that Mary 

It sounds like any relationship or trust that you had had now gone 

Ask building control what remedial measures need to be taken to satisfy them 

Then put it in writing what needs to be done to get you back on track Giving him 30 day to sort it out Or you will bring in another builder at his expense and take him to small claims court if need be 

I’m guessing he will know all about small claims court

 

There are plenty of good builders out there But as many poor ones also The later of quite skilled at making the customer feel like they are in the wrong or don’t know what they are talking about  

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@nod  sorry I am a bit slow here, lack of sleep, do you believe the insulation would not have passed building control?  I already know that dividing the garage, putting in a radiator and a window needed approval, I didn't realise the insulation would also?  if that's true then it does help!

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