Roof 'felt' is actually a plastic membrane

adocholiday

Hi all,

Bit of a text wall here but please bear with me. I recently bought a house that was built in 2001. The gutters needed to be replaced and the guy doing the gutters advised that he noticed that the roof felt was actually a plastic membrane. He said it was more like something that you'd see in a damp proof course or in a shed and that it was causing a mould to grow on our roof timbers and rotting in places. It's also contributing to condensation in the house. He said the remedy here would basically be an entire re-felting job and replacing/repairing any damaged timber, which would not be cheap.

Needless to say I got a fright with this and had our engineer come for a look. He measured the moisture levels in the timbers and they said they were all ok, in the ~10% range but that we should vent the space and that a re-felt would be a last resort.

Now it's worth noting that the house is a bungalow with a currently unused converted attic, so there's a knee wall of uninsulated plasterboard on each side with a crawl space behind it. In the crawl space we can see that there is rigid insulation board between the rafters, and fibreglass insulation in the cavity between the floor and ground floor ceiling.

The engineer has recommended that:

1. We completely remove the rigid insulation board between the rafters to allow air to circulate around the timbers.
2. If the timbers are ok then we can leave as is, otherwise assess what needs repair/replacing.
3. Replace the plasterboard walls with insulation backed board.
4. Replace the fibreglass insulation in the floor with a thicker layer of mineral wool.
5. Put a vapour barrier up in the crawlspace to stop vapour condensing on the plastic.
6. Put a vent on each gable on each side of the crawl space (so 4 in total).
7. Put vent tiles in the roof.

What I would like to know is if anyone with experience in roofing would have any experience of this or any other suggestions? One of the things I'm particularly unsure of is removing the rigid insulation boards from the timbers. Anything I've read about attic insulation mentions insulating that space. We do eventually want to use the space so I'd like it to be as comfortable as possible and I want to make sure that whatever we do, we do right.

I can provide more info if needed, many thanks.

Edit: I think it's something like this synthetic stuff: https://www.globalplasticsheeting.com/our-blog-resource-library/topic/roofing-underlayment

dathi

https://www.youtube.com/watch?v=c7-whPGx6BU

is it something like this that he hasn't seen before

adocholiday

dathi wrote: »

https://www.youtube.com/watch?v=c7-whPGx6BU

is it something like this that he hasn't seen before

No it's actually like big sheets of plastic rolled onto the roof where traditionally a felt would be used. I've added a link to what I think is the material in my OP

Calibos

Going on what I've learned here, you only need to do anything insulation and ventilation wise if the entire roof was done with a vapour impermeable felt. If its just a small section with the PVC product Daithi linked to then you dont need to do anything.

How much exploratory work did the engineer do? Did he remove a section of the insulation board between the rafters in the eaves storage space to get a look at the pvc felt to see how far up the roof it extended?

I have a similar issue to what you might potentially have in that my felt is 40yo vapour impermeable bitumen felt but my renovation builder back in 2010 did not put vent cards/leave a 50mm ventilation gap between insulation and underside of impermeable bitumen felt from eaves to ridge vents like he should have. The lads here mostly lost interest in my thread when i said there was no way I was lifting the entire slate roof to replace the felt with a vapour permeable felt or pulling down the ceilings to retrofit vent cards from the underside. Ended up coming up with a clever solution myself for my particular situation that I'm pretty sure takes everything into account but the lads seemed averse to commenting on it/'sign off on it' (liability concerns probably)

adocholiday

Yeah the synthetic layer goes all the way up the roof so no vapour permeability in the roof at all, and the rigid insulation boards are basically pushed right up against it so very similar situation to your own. Luckily I don't need to go pulling down ceilings or anything though to vent it, I already planned to replace the existing plasterboard with the insulation backed boards and I have full access to the crawl space so I can add wall vents, vent tiles, redo insulation etc etc. with relatively little hassle. My concern is that I'll overall lack insulation in the attic space and it will be freezing, or that venting won't be adequate and I'll spend all this money and still end up re-felting (at an approx cost of over 7 grand!)

Calibos

adocholiday wrote: »

Yeah the synthetic layer goes all the way up the roof so no vapour permeability in the roof at all, and the rigid insulation boards are basically pushed right up against it so very similar situation to your own. Luckily I don't need to go pulling down ceilings or anything though to vent it, I already planned to replace the existing plasterboard with the insulation backed boards and I have full access to the crawl space so I can add wall vents, vent tiles, redo insulation etc etc. with relatively little hassle. My concern is that I'll overall lack insulation in the attic space and it will be freezing, or that venting won't be adequate and I'll spend all this money and still end up re-felting (at an approx cost of over 7 grand!)

In my case, I have plenty of insulation (200mm Fibreglass roll) between plasterboard ceiling and bitumen felt. I too have eaves access and partial bedroom ceiling access from my own stooped/crawl space and also safe access and working environment at my Ridge. My DIY non destructive retrofit vent card solution is strips of reasonably stiff 3mm fiberboard with 1in holes perforated all over with a spade or forstner bit with a vapour permeable but windproof membrame glued onto the strips. Several 50mm semi circle spacers affixed. When pushed up into the bedroom ceiling space from the crawl space the Spacers shouldn't tear the bitumen felt, create the 50mm ventilation run, the 'stiff' fibreboard compresses the fiberglass insulation as it goes. The perforations in the fiberboard let moisture percolate to the ventilation run to be carried away, the vapour permeable membrane glued to the fiber board prevents all the heated air in the insulation being blown out. I'll fit ventilated ridge tiles myself. I'll end up with 150mm effective insulation in the ceiling. 25% of a homes heat is lost through the ceiling/roof and like 80-90% of insulation efficiency is in the first 150mm so thats plenty for me. Its why I was never arsed fitting joist stilts or any of that malarkey to get 300mm in the cold attic. 100mm fiberglass between ceiling joists and 50mm insulation backed attic flooring for me.

BryanF

adocholiday wrote: »

Yeah the synthetic layer goes all the way up the roof so no vapour permeability in the roof at all, and the rigid insulation boards are basically pushed right up against it so very similar situation to your own. Luckily I don't need to go pulling down ceilings or anything though to vent it, I already planned to replace the existing plasterboard with the insulation backed boards and I have full access to the crawl space so I can add wall vents, vent tiles, redo insulation etc etc. with relatively little hassle. My concern is that I'll overall lack insulation in the attic space and it will be freezing, or that venting won't be adequate and I'll spend all this money and still end up re-felting (at an approx cost of over 7 grand!)

Ok. The impermeable ‘plastic sheet’ should be on the warm side of the insulation.

What you have is the plastic sheet on the cold side of the insulation

This means warm air, that has moisture in it, migrates from your house, past the insulation and condenses on the cold plastic sheet.

adocholiday

@Calibos any chance you might have pics or even an illustration? Just can't quite put together your solution in my head.

@BryanF would it really go on the inside of the insulation? Wouldn't any water ingress from the roof then just destroy the insulation? The engineer seemed to think that it was in the correct place, but you're correct it's the vapour condensing on the cold plastic that's the problem. The engineer's opinion was to insulate the knee wall as much as possible, and to insulate the cavity between the floor and ground floor ceiling as much as possible, and put a vapour barrier up then to prevent as much moisture as possible getting into the roof space. Any moisture that does get in would be handled by really good ventilation. It sounds like a solid plan to me, it just feels counter intuitive to remove insulation from the rafters when pretty much any insulation guides will tell you to insulate the rafters!

Calahonda52

Strip the roof and build up the insulation from outside, get some ideas here:
https://www.ecologicalbuildingsystems.com/Ireland

This will simply the work in the long run and make the crawl space much more usable

Any pictures?

adocholiday

Calahonda52 wrote: »

Strip the roof and build up the insulation from outside, get some ideas here:
https://www.ecologicalbuildingsystems.com/Ireland

This will simply the work in the long run and make the crawl space much more usable

Any pictures?

Strip the roof as in re-felt, re-tile, and re-insulate? The price I got for that was in the 7k-8k range minimum, I simply don't have that kind of money right now. It's probably the correct solution in the long term but right now I need to just do a 'good enough' cost effective measure.

I don't have any pics right now but should be able to upload in the next day or 2

hesker

I’m not a building professional but have read a bit around this before. So here is my input. Others can critique if they wish

You need to do some reading up on Cold Roof and Warm Roof and understand the differences and requirements.

You have a cold roof. Your basic problem is most likely there is no ventilation to the roof timbers because the insulation has been pushed right up against your roof felt. I’ve no idea what your soffitt vent setup is like.

Installing a vapour barrier on the warm side of the insulation is a vital step in preventing moisture laden air getting up to the timbers and condensing. However an equally important step is ensuring there is a min 50 mm gap between insulation and felt because it is impossible to 100% seal a vapour barrier.

You will see details of vapour permeable membranes being sold as replacement for roof felt allowing insulation to be pushed right up with no gap but plenty of accounts of this not being reliable or good practise. There was a big discussion on this topic here previously.

You probably have more than one solution but you should start by fully understanding the problem.

Calibos

adocholiday wrote: »

Strip the roof as in re-felt, re-tile, and re-insulate? The price I got for that was in the 7k-8k range minimum, I simply don't have that kind of money right now. It's probably the correct solution in the long term but right now I need to just do a 'good enough' cost effective measure.

I don't have any pics right now but should be able to upload in the next day or 2

LOL. I got the same answers for the most part on my similar thread from last week. The lads lost interest when I said, no way no how could I afford to lift the roof and re felt or rip out the ceilings to install vent cards from the inside.

Heres my non destructable Vent card retrofit idea.



From my crawl space I can reach into the bedroom ceiling over the knee wall. I'd fabricate a load of these. Push them up underneath my bitumen felt and they'd compress the fiberglass insulation as they go and create the 50mm ventilation gap. I'd connect the next section to the first and keep pushing until they reach the Ridge and do that between every rafter except for those blocked by the framework for my two velux. Between the rafters above the velux framework I'd have to wait till I have lifted the ridge tiles to replace with ventilated ridge tiles before I could push some of my DIY vent cards down to the velux framework from the ridge.

(if I found my semicircle spacers were ripping the bitumen felt I'd instead buy and use a load of little plastic furniture wheels as spacers/rollers)

GreeBo

BryanF wrote: »

Ok. The impermeable ‘plastic sheet’ should be on the warm side of the insulation.

What you have is the plastic sheet on the cold side of the insulation

This means warm air, that has moisture in it, migrates from your house, past the insulation and condenses on the cold plastic sheet.

+1

OP it should be the case that the only source of moisture on the inside of this plastic sheet is condensation from your warm attic.

So you should be ok if you solve this problem which you can solve by essentially rebuilding the internal attic space and adding the vapour barrier on the attic space side of the insulation.

Personally I would strip the attic room and get it as a ventilated cold space to allow the timber to dry before I would try to get the attic back as a warm space.

Cost is going to be your decider, but either way you need to get a vapour barrier on the warm side of the insulation or anything else you do is still going to suffer from condensation.

GreeBo

Calibos wrote: »

LOL. I got the same answers for the most part on my similar thread from last week. The lads lost interest when I said, no way no how could I afford to lift the roof and re felt or rip out the ceilings to install vent cards from the inside.

Heres my non destructable Vent card retrofit idea.

<snip>
From my crawl space I can reach into the bedroom ceiling over the knee wall. I'd fabricate a load of these. Push them up underneath my bitumen felt and they'd compress the fiberglass insulation as they go and create the 50mm ventilation gap. I'd connect the next section to the first and keep pushing until they reach the Ridge and do that between every rafter except for those blocked by the framework for my two velux. Between the rafters above the velux framework I'd have to wait till I have lifted the ridge tiles to replace with ventilated ridge tiles before I could push some of my DIY vent cards down to the velux framework from the ridge.

(if I found my semicircle spacers were ripping the bitumen felt I'd instead buy and use a load of little plastic furniture wheels as spacers/rollers)

How is this addressing the lack of vapour barrier?

Calibos

adocholiday wrote: »

@Calibos any chance you might have pics or even an illustration? Just can't quite put together your solution in my head.

@BryanF would it really go on the inside of the insulation? Wouldn't any water ingress from the roof then just destroy the insulation? The engineer seemed to think that it was in the correct place, but you're correct it's the vapour condensing on the cold plastic that's the problem. The engineer's opinion was to insulate the knee wall as much as possible, and to insulate the cavity between the floor and ground floor ceiling as much as possible, and put a vapour barrier up then to prevent as much moisture as possible getting into the roof space. Any moisture that does get in would be handled by really good ventilation. It sounds like a solid plan to me, it just feels counter intuitive to remove insulation from the rafters when pretty much any insulation guides will tell you to insulate the rafters!

The vapour impermeable membrane between the slates and insulation means that vapour getting through the ceiling and insulation condenses on the membrane and leaves the insulation soaked reducing its efficiency, causing mold growth and eventually rotting the rafters. Anytime you use a vapour impermeable membrane on the cold side of the insulation you have to have a 50mm ventilation gap between that membrane and the insulation to carry away the moisture before it condenses on the underside of the membrane and drips back onto the rafters and insulation. My issue was the bitumen Felt in my roof is vapour impermeable but my renovation builder in 2010 installing fiberglass insulation never created that 50mm ventilation gap with vent cards which as you know I hope to retrofit myself non destructively whereas the lads here will only suggest a very expensive do-over. At least my builder did fit a vapour impermeable membrane/sheeting to the warm side of the insulation behind the plasterboard ceiling as there would have been no way for me to retrofit that otherwise.

Your engineer is suggesting moving your crawl space outside of the insulation/vapour envelope by suggesting you insulate and install vapour barrier in the crawlspace floor and knee wall and cross ventilating it with vents on the gable walls. I'm a bit confused about that too. How does that solve the problem of no ventilation gap between each rafter underneath the vapour impermeable roof membrane on the rest of the roof up to the ridge??? Does your crawl space not have access/venting to the eaves/soffits?

GreeBo

Calibos wrote: »

. How does that solve the problem of no ventilation gap between each rafter underneath the vapour impermeable roof membrane on the rest of the roof up to the ridge??? Does your crawl space not have access/venting to the eaves/soffits?

Think the OP already answered that?

adocholiday wrote: »

The engineer has recommended that:

1. We completely remove the rigid insulation board between the rafters to allow air to circulate around the timbers.

Calibos

GreeBo wrote: »

How is this addressing the lack of vapour barrier?

OP's or mine??

Don't think OP has mentioned whether he has a vapour barrier on the warm side of his insulation behind the plasterboard ceiling.

I do have a vapour barrier on the warm side of mine. I can feel it behind the plasterboard when I reach over my crawl space knee wall and push my hand under the fiberglass insulation.

OP has a modern vapour impermeable weather proof felt under his slates whereas I have a much older bitumen felt but which is also vapour impermeable.

It seems in both our cases, our rafter insulation was installed behind and right up against our impermeable roofing felts without the required 50mm ventilation gap from eaves/soffits to ridge.

Calibos

GreeBo wrote: »

Think the OP already answered that?

That assumes he has insulation board all the way to the ridge and not fiberglass roll beyond the knee wall of the crawl space. If he does and we assume he has 200mm rafters then if its two 100mm layers, maybe he could pull one layer out and push back up 50mm giving him 150mm insulation board and 50mm air gap.

TBH, I think OP needs to do some inspections himself. For all we know, he actually already has a 50mm gap between roof membrane and insulation board if thats what he has all the way up to the ridge. In fact, that, combined with a lack of eaves/soffit ventilation is the only way the engineers suggestion to take the crawl space outside the insulation/vapour envelope and cross ventilate it with vents on the gable walls makes any sense.

Anyway, point is. I am not saying my solution is applicable to his situation, I initially posted more in terms of the broader similarities of our situation and the fact that the only answers either of us are/were getting in our respective threads was re-roof or re-slab and skim our attic bedrooms to retrofit for €€€€€ and the experts wont discuss any other possible options. I only posted a picture of my solution because OP asked for it. I did not nor am not suggesting it was applicable to his situation.

hesker

Calibos wrote: »

(if I found my semicircle spacers were ripping the bitumen felt I'd instead buy and use a load of little plastic furniture wheels as spacers/rollers)

That would be my concern. You will be putting a lot more pressure on the felt than on the insulation due to design and contact points.

How will you know you have a rip or not at the apex.

GreeBo

Calibos wrote: »

the fact that the only answers either of us are/were getting in our respective threads was re-roof or re-slab and skim our attic bedrooms to retrofit for €€€€€ and the experts wont discuss any other possible options.

Thats because with any other options you don't know the quality of the finish.
You dont know if you have a gap or a tear or whatever.

Calibos

hesker wrote: »

That would be my concern. You will be putting a lot more pressure on the felt than on the insulation due to design and contact points.

How will you know you have a rip or not at the apex.

GreeBo wrote: »

Thats because with any other options you don't know the quality of the finish.
You dont know if you have a gap or a tear or whatever.

I hear ya guys and its great you are engaging. I wanted critique of my idea in my own thread but the lads there switched off for the most part as soon as I said I didnt have the thousands needed for a re felting or re slabbing and skimming.

I was thinking only in terms of catching the bitumen felt with the spacers but of course you are right. There would be pressure points doing it either way I suggested that might crack it if its brittle. (Best do it next heatwave! ) However, the telescopic attic hatch pole I already own for access to the cold attic springs to mind. Push that up from my over knee wall access and press down on the fiberglass to create the gap. Then my DIY vent cards to maintain it...but without them needing to compress the fiberglass as they go creating the pressure points as you say.

An inspection camera fitted to the end of the telescopic pole to check the felt/see where the pole is going and helping guide it away from the felt. An inspection camera will be a lot cheaper than the 8 grand to re roof.

hesker

Calibos wrote: »

An inspection camera fitted to the end of the telescopic pole to check the felt/see where the pole is going and helping guide it away from the felt. An inspection camera will be a lot cheaper than the 8 grand to re roof.

Yeah I thought of that too after posting. I say give it a go and do your inspections during a good downpour. Compressing your insulation will reduce its effectiveness as you might be aware. You might find it difficult to push those spacers all the way up but you won’t know until you try.

Calibos

hesker wrote: »

Yeah I thought of that too after posting. I say give it a go and do your inspections during a good downpour. Compressing your insulation will reduce its effectiveness as you might be aware. You might find it difficult to push those spacers all the way up but you won’t know until you try.

8/9inch rafters and I can see/feel the fiberglass insulation fills the space. I do understand that my 200mm of insulation when compressed to 150mm will only have the R value of 150mm roll. Like I said in a previous post though, I'm happy enough with that given 80-90% of insulation efficiency is in the first 150mm anyway.

TBH, I'll probably forget about the semi circle/furniture wheel 50mm spacers now after your observation about pressure points on the bitumen felt. I'll probably just run 50mm tall strips of wood along the length of the vent cards one on each side. I'll also mold/bend the front of the first vent card up like the bow of a boat to ride over the pre-compressed fiberglass and prevent it catching on the fiberglass

sydthebeat

Interesting idea but the membrane in that detail is a compete waste of time. Membranes need to be continuous and salable.

Also. You're reducing your insulation value by 25%.....probably actually 33% as in reality I think you actually have 150 rafters and not 200...200 is an off standard rafter depth which wouldnt have been available off the shelf

GreeBo

Calibos wrote: »

8/9inch rafters and I can see/feel the fiberglass insulation fills the space. I do understand that my 200mm of insulation when compressed to 150mm will only have the R value of 150mm roll. Like I said in a previous post though, I'm happy enough with that given 80-90% of insulation efficiency is in the first 150mm anyway.

TBH, I'll probably forget about the semi circle/furniture wheel 50mm spacers now after your observation about pressure points on the bitumen felt. I'll probably just run 50mm tall strips of wood along the length of the vent cards one on each side. I'll also mold/bend the front of the first vent card up like the bow of a boat to ride over the pre-compressed fiberglass and prevent it catching on the fiberglass

R value will be less again as you are removing air by compressing it.

If you compressed it until solid, say 50mm then it wouldn't have the same r value as 50mm off the shelf.

Calibos

sydthebeat wrote: »

Interesting idea but the membrane in that detail is a compete waste of time. Membranes need to be continuous and salable.

Also. You're reducing your insulation value by 25%.....probably actually 33% as in reality I think you actually have 150 rafters and not 200...200 is an off standard rafter depth which wouldnt have been available off the shelf

Can you explain what salable means (google was no help) or was that a typo? Just to clarify again. I have a vapour proof plastic sheeting behind the ceiling plasterboard on the warm side of the insulation. I have a bitumen felt under the slates. I have 200mm cavity between ceiling plasterboard and Bitumen felt, currently completely filled with Fiberglass. I just measured directly by reaching over the knee wall with a measuring tape, its definitely 200mm. I already knew this without measuring though because of this construction photo from 2010. The original Victorian rafters where 100mm/4in (measured from Eaves storage area). The new rafters are twice the depth of the old.

The purpose of the DIY vent cards was to create/maintain a 50mm ventilation gap from the eaves/soffits to the Ridge. The only reason I included the vapour permeable membrane to the DIY Vent card was as a wind proof membrane to stop the warm air trapped in the insulation being blown out but still allowing any moisture getting through the actual vapour barrier to escape to the 50mm ventilation gap.

Would I be correct in assuming that salable was a typo for sealable? ie. you reckon its a waste of time if it wasn't stapled/sealed to the sides of the rafters? Would a vapour permeable windproof membrane really need to be 100% hermetically sealed to do its job? Remember, as it stands right now wind can blow straight through all the insulation from eaves/soffits to Ridge. Even if my windproofing solution is draughty because its not 100% sealed between rafters, its still going to be a hell of a lot better than the current situation and dramatically reduce/slow down air movement within the insulation?

GreeBo wrote: »

R value will be less again as you are removing air by compressing it.

If you compressed it until solid, say 50mm then it wouldn't have the same r value as 50mm off the shelf.

Thats not what I understood. I always heard it framed in terms of there being no point spending extra on 200mm and then compressing it into a 150mm space because it would only have the effective R value of 150mm, so save money and put in 150mm to begin with.

This Link and several others after googling seem to bare this out??

GreeBo

Presume it was sealable, as in it can be jointed with no loss of performance.

Calibos

GreeBo wrote: »

Presume it was sealable, as in it can be jointed with no loss of performance.

So is Sydthebeat and you saying this particular detail on the DIY vent card is a total waste of time unless 100% sealed to the rafters. Its just that I find that hard to believe. Is this a case of 'perfection is the enemy of the good' here?

Sidenote:

Last nights storm was a good test of the attic conversion bedroom. After the second to last winter storm I filled around pipe penetrations from the gas boiler to the cold attic space, sealed around the boiler flue where it penetrates the ceiling plasterboard. (both areas where I could feel cold draughts) I also replaced the East facing ensuite bathroom extractor with an ICON unit with closing Iris draught excluder. The exterior gravity flaps were always useless and my first attempt at a solution to this 4in hole in the building envelope which was an inline Manrose backdraught flap was also useless. The simple pressure differential between inside and outside held the flaps open even without the fan on. The ICON iris has solved it.

Knew these measures had been successful during the last Winter storm. While I woke up to a freezing bedroom because the major draughts in the eaves storage space have yet to be dealt with but when I opened the bedroom door and walked out onto the little landing and into the ensuite I could instantly feel the temperature difference when I opened the door. This used not be the case. If the bedroom was freezing, the little landing/ensuite was also always freezing.

After last nights storm and a coincidental bout of insomnia, the bedroom stayed comfortable all night long. The difference?? I had wrapped a towel around the Eaves storage Space access door and forced it closed, closing off the bedroom from draughts coming from the eaves storage.

I'm now even less concerned with eventual R values of compressed ceiling insulation or the air penetration from the eaves/soffits from driving warm air out of the insulation.

So I arrive back where this all began. Knowing that the major cause of this bedroom being uncomfortably cold is the major draughts into the bedroom from the eaves/soffits/eaves storage area and this also being the cause of being able to literally hear people whisper in the street below. Back to knowing that I need to seal/vapour proof the eaves storage area properly and plasterboard it out to block much more of the sound from outside and finally back to my only real concern which is that I didn't want my draught and sound sealing solutions to have a knock on effect and trap moisture in the ceiling and cause the roof to start to rot.

To wit....Should I just forget about the DIY vent cards altogether and before I redo the vapour barrier and plasterboard in the eaves storage area, I should just compress the insulation between the bedroom ceiling rafters with the telescopic pole I talked about earlier in order to create about a 50mm gap between insulation and bitumen felt. ie. last nights storm seemed to prove that warm air being blown out of the insulation didn't make much difference to the comfort of the room anyway.

GreeBo

A barrier isn't a barrier if it has gaps.

A bucket with a hole in it doesn't hold water.
Insulation that's perfect other than 1 section might as well not exist. This is why you need someone, DIY or otherwise who knows the importance of detail in this area.
Spending tens of thousands on materials only to have them installed incorrectly, even if it's only 5% then you have wasted money.
Cold bridges, air gaps, gaps in barriers all can seem insignificant but they are crucial to performance.

Calibos

GreeBo wrote: »

A barrier isn't a barrier if it has gaps.

A bucket with a hole in it doesn't hold water.
Insulation that's perfect other than 1 section might as well not exist. This is why you need someone, DIY or otherwise who knows the importance of detail in this area.
Spending tens of thousands on materials only to have them installed incorrectly, even if it's only 5% then you have wasted money.
Cold bridges, air gaps, gaps in barriers all can seem insignificant but they are crucial to performance.

Well then its wasted money from 10 years ago in my case then. Not that the amount of fiberglass roll or vapour barrier sheeting in our renovation cost more than a grand or so anyway. Yeah, its a shame it wasn't done right at the time so that spend was somewhat wasted. I know there was 10 years of heatloss from this bedroom to take into account too, but I can't imagine that adds up to a fortune either.

Put it this way, other than this draughty attic conversion/boiler cupboard/ensuite, the rest of this Victorian House performs well with its 18-24" thick walls with huge thermal mass, with new insulated ground floor slab, new doors and DG Wooden Sash windows with massive solar gain from 17 of its 19 Windows and Doors being South and West facing. I DIY replaced the old Multizone HW/CH Controller with a Multizone HIVE during the Summer and have been monitoring the temperature graphs this Winter. Even before any of the draught exclusion works already performed by me in this attic conversion, I could see that the temperature of the groundfloor and first floor CH zones only drops between 1.0-1.5ºc overnight from 12:00am till 8am when the Heating is scheduled to come back on. Remember, thats the temperature drop with the attic conversion leaking like a sieve like it has been the previous 10 years.

Last nights major Winter storm it dropped 1.3ºc. The Hive is already saving us money on CH simply by virtue of being Thermostatically controlled between 8am and Midnight whereas the old controller had no thermostats in any zone. I hardly ever hear the Boiler running.

Point is. I literally don't care about cold bridging or R-Values at this point. The house is now comfortable temp with no extremes all day long thanks to the HIVE. its not dropping in temp by much overnight when the CH is off, the house has no mold or damp issues evident nor any evidence of issues in the poorly/non ventilated cold attic even with uncovered cold storage tanks, no evidence of mold or damp in the attic conversion ceiling which is currently inspectable from the eaves storage space.

At this point, literally all I care about now is to prevent any of my works in the attic conversion eaves storage area to stop the major draughts and sound penetration from creating/causing problems down the line to the roof/rafters of the attic conversion bedroom.

The more I read about insulation and BER A ratings, passivehaus etc and the costs thereof, the more I think that they all have a massive case of rapidly diminishing returns. ie. Works/Spend on insulation and air tightness etc are worthwhile up to a point from a cost/benefit analysis perspective but the industry/regulators just don't know when to stop. EG. Insulation gets 90% of its efficiency in the first 150mm, €80,000 Deep Retrofit costs for a 3 bed semi that'll take 50 years to pay for themselves, A solar Water Heating setup costing €5000 that would save me about €30 a month and take 15 of its 20 year lifespan to pay me back. But what about your Carbon Footprint Calibos!!!! The carbon footprint reduction of all these A rated homes will be eclipsed by the carbon footprint reduction from the switch to electric cars which will be nearly complete within 10 years long before any of the A rated homes have paid back their owners. Forget about the public's irrational fear of the answer to Global warming which is Nuclear Fission Power Generation and I know Nuclear Fusion is always 30 years away but it'll definitely be a thing long before these a rated retrofit folks have been paid back. At that point we'll have cheap electric carbon neutral Home heating and transport all the while many peoples A rated retrofit costs still haven't paid them back. RANT OVER! LOL

Lumen

Calibos, you're ranting that your generally well performing old building doesn't need a deep retrofit. Well...OK.

Passivehaus is not a retrofit protocol, it's a standard almost exclusively used for new buildings, where the incremental cost over a normal build is much less than the cost of a retrofit to any standard on an old house. So I don't know why you're conflating these.

The fact that the part of your house which is giving you problems is the newest part isn't surprising. Many houses have been ruined by inappropriate extensions and "improvements". It's generally the way of things, like aftermarket car components. But that's got nothing to do with the appropriateness of current building regs or passivehaus to new stock.

As for BER ratings, that system is fairly crap for several reasons, but it is quite good value. I'm not sure what the alternative is short of compulsory heat loss survey including blower door testing, but that would introduce significant costs to the seller and at some stage caveat emptor applies. In any case my own house's BER suggested annual heating cost of 5k and that was about right when we moved in, so the BER isn't necessarily inaccurate. But if I could hit A3 I'd save 4k/year, which is a big chunk of change.

IMO deep retrofits should be funded by 30 year government bonds, which could be funded at 1.6%, and then the cost part-recovered by a tapering levy on the MPRN for the same duration at the same rate, with the bonds paid off by increased tax take from the economic stimulus. In my case a 200k retrofit would cost me 3200/year in the first year which would represent an immediate saving, but without that kind of approach it's not cost effective since banks charge 3% and won't fix over the long periods required to pay back these investments.

Nuclear might produce less CO2 but it's more expensive than the alternatives so won't help occupiers of poorly performing houses facing high energy costs.

adocholiday

Hi all,

OP here, only catching up now. So I've checked a bit more over the weekend. There does in fact seem to be a 50mm or so gap between the rigid insulation boards between the rafters and the synthetic felt. Couldn't see much in terms of condensation or mould on the timbers thankfully but there was definitely some and it's something I do want to remedy.

The bottom image in this link illustrates what we currently have now, with additional insulation under the floor. The top image illustrates what the engineer is asking us to do, with a vapour barrier on the back of the insulation (i.e. between the insulation and the rafters). We'd also install additional ventilation on the gables and completely remove the rigid boards between the rafters. My questions are rather simple:

1. Should that be sufficient to ensure that the timbers stay relatively dry and reduce the risk of rot?
2. Will the new insulation setup be enough to ensure that the upstairs rooms retain adequate heat? Obviously provided that the insulation is the correct size etc. I'll be getting a professional insulation company in to do it because we want to get the walls pumped also.

If the answers to both of those questions are yes then I'm completely satisfied. It just seems that there are few people experienced with synthetic felt so if there's something else for me to consider that I haven't mentioned then I'd like some input if possible.

Edit: Found a better drawing with the left hand side particularly showing the proposal of the engineer. We can't have soffit vents so gable vents needed. http://energysmartohio.com/uploads/content/HalfStoryAFTER_600.gif