Roof insulation options - Large Vented Eaves

[GeddyMortgage]

Hi all,

I recently followed some great advice on this forum to insulate my suspended ground floor. Awful job, but in completion the amount of difference it's made has been incredible. Off the back of that I've decided to look at what else I can insulate to further increase the thermal efficiency of this property.

So the next place I wanted to look properly at was the loft space on the top floor. The property does already have 3 rooms situated together toward the middle of the top floor, and the loft space surrounds them at the edges of the top floor... if that makes sense.

I noticed in the loft space it already has a good deal of insulation on between the floor joists as shown on the picture below. But also noticed the voids between the roof joists are without insulation. Am I correct to assume this can and should be insulated?

One other thing I noticed was at the far edges of the loft space, I can see daylight and a considerable draft coming through up through the vents in the eaves, see video and photos below.

Is there anything I need to be aware of with regards to insulating the roof joists when considering these eaves vents? Also do I have any options to insulate those drafts in the eaves? I can appreciate why they shouldn't ever be blocked, but sort it's got me thinking that even if I insulate the void between the roof joists....the cold air from the eaves vents will be coming up below them anyway and I guess massively negating any benefit i'd see by insulating said roof joist voids?

Video will explain better - Loft and eaves Video

thanks very much,

Ged

 

[robinbanks]

If by "roof joists" you mean the sloping things in your pic, to which the white sheet is attached, then the response to "can and should I insulate them" is "you can, but you wouldn't".

The loft as pictured/videod is a cold roof construction; a thick blanket of wool rests on the loft floor, and below this are the house rooms. Above this is the rain cover for the house. A breeze blows through the loft, keeping condensation at bay. The whole of the materials that comprise the roof are thus at the same temperature as the world. Insulating them would be fruitless as The space underneath them is the same temperature as the outside

If you have plans to change the house to have a warm roof construction, then you would insulate, but you'd typically do that as part of a loft conversion to make the loft into a usable room

The way part of your post is written it implies that there are some habitable warm rooms that are at the same level as this area you have videoed. That being the case your roof construction may be part warm and part cold. This isn't a problem; the overall notion is that all the warm parts of the house are on one side of insulation and world air is on the other. If you have rooms in the loft but still have other parts of loft that are like the video, then the insulation should start on the loft floor, run up the wall separating the warm room from the loft, and over the top

In the picture below, R are heated rooms, W is world temperature air, the orange line represents insulation of the thermal envelope and the roof is either blue or red depending if it is cold or warm construction

For best performance the insulation should be continuous. This isn't always possible as things like roof trusses have to* bridge it, but careful detailing can minimise heat losses around the joints

For example, below might be a typical, if careless detailing:

The cavity wall insulation (vertical orange) fills the wall, but to leave a huge eaves vent the loft insulation (horizontal orange) doesn't join up with it/doesn't go far enough to the roof edge to inhibit heat loss at the room edges of the ceiling. Something should be done to maintain ventilation of W above the insulation, but also ensure the thermal envelope is as unbroken as possible by improving continuity of insulation

* I say "have to" - that can be designed out but it is usually done at planning/original construction time. Removing built-in thermal bridges after the fact is usually prohibitively expensive

 

[robinbanks]

Also noted you have toy boxes etc in the loft; strive to avoid compressing the wool as it reduces its performance. Typical construction these days is to have the area between the joists that support the downstairs ceiling filled with wool and then have more wool over the joists up to an overall depth of about 300mm. If you want to use the loft for storage you fit "loft legs" onto which board flooring is installed and the flooring carries your stored items, the loft legs prevent compression of the wool

 

[GeddyMortgage]

Thanks for the detailed response, that does very accurately describe what I thought the setup was to be fair. Though without taking a hammer to it...I've got no way of knowing for sure whether the 'ceiling' in the top floor rooms have insulation boards in the void between the plasterboard and the roof tiles...though i'd very much hope so.

The rooms on that top floor are now the coldest in the property by some way... I presumed its because they're at the same height/ higher than the vents in the eaves. So constantly have a very cold circulation of air surrounding them...…separated only by the a thin stud walls and insulation boards in those stud walls....

....For the most part, on the other side of the walls in the top floor rooms, they have 100mm of insulation board or so....Though quite alot of places on the right hand side where the boiler cupboard is.... the stud walls there just aren't insulated at all...

I've tried to show it on the diagram below.....

:-For the stud walls that already have 100mm insulation board I assume that's as good as it's gonna get? Or can I add some roll over the top of this for even more thermal performance?

:-For the walls that don't have any....that's an obvious target area to add some boards ofcourse.

Though will either of those options above only help insulate those top floor rooms or could more insulation there help the rest of the house at all through having more resistance to cold air getting into the 'liveable space' .....Weighing up bang for buck.

and some images what it looks like on the other side of the stud walls.... RE: some with insulation, some not.

 

[Why Not Indeed]

Can't quite tell if those copper pipes are in the "cold side" or not, but if they are then I would have thought lagging them would be worthwhile.

 

[robinbanks]

If those pictures are taken by you standing in the cold eaves area and photographing the back side of the walls of your loft rooms then it would appear that there is much you can do to improve the insulation, especially if it is not continuous as implied by the diagram

If you want to know whether there is insulation above the ceiling you could try and find an area in the eaves where you can see up the underside of the roof slope (put your head so it's touching the white roof felt and see if you can see the other side of the ceiling plasterboard), or use a small drill and screwdriver to make a hole about 15mm deep in the ceiling plasterboard and then stick the screwdriver through and wiggle it around : you'll be able to feel the insulation inhibiting the movement of the screwdriver / hear it crunching as you push the driver into it if it's there. It's easy to polyfilla over a small hole

That said, if the company that made the same abortive attempt at insulating the walls did the ceiling, I think I'd be drillling several inspection holes using a hole saw to have a better look/feel for a draught on a breezy day. If there is insulation tucked up against the plasterboards and no draught you may be ok. If there is boards and draught it implies they're poorly fitted (gaps at the edges or bowed) and world air is reaching the plasterboard anyway meaning the insulation is fairly useless. Holes sawed neatly are easy to refill by placing the cut piece back in place and fillering over it. If you locate the sloping roof joists (rafters) using a magnet to find the screws holding the plasterboard up, and you drill a large enough hole that you'll be able to see the side of the rafter you'll be able to see how well the insulation has been fitted at the edges. The best case is, having located a few screws to work out the rafter line, if you saw the plasterboard away and all you see is insulation then it means the rafters have been insulted over as well as between. I get the feel

When refitting the cut out piece you just screw it back to the rafter and fill the cut slots in. If you've drilled a hole in a non rafter area and there is insulation above, glue the piece to the insulation using expanding foam.

Also give a thought to borrowing or buying an infrared camera and looking at the temperature of surfaces that you know have insulation behind them vs areas you aren't sure of - it can be a no-destruction way of sounding out which areas need closer inspection

If you don't find well fitted insulation up there, brace yourself for either taking the ceiling down (not that bad of a job especially with patience, a magnet and a multi tool to cut the board edges into neat sheets), or if height isn't a problem, boarding insulated plasterboard over it. I'd have a small concern (again judging by the walls) that there isn't any vapour control layer (a sheet of plastic) sandwiched between the plasterboard and the insualtion, stopping human generated moisture (cooking, drying clothes, breathing etc) making its way through the plasterboard (it does unless the pb is foil backed) and condensing on eg the cold rafters, meaning they can end up soaked which impacts their longevity.

Edit; as evidenced by this pic:

There is insulation above your ceiling (in at least some areas) but:

* there's a huge gap between the wall insulation and the ceiling insulation- that's a ****ty detail
* the ceiling insulation isn't bonded to the plasterboard, so if there is a gap that air can get down it it starts to make the insulation pointless if world air can cool the back side of the ceiling plasterboard
* even if there isn't a draught gap the plasterboards are screwed direct to the rafters; if you looked at this room within an infrared cam it'd look like a prison of cooler bars for the rafters and warmer blocks of insulation between. Wood has some insulative value but it's no celotex, which is why we typically look to board insulation over rafters as well as between them

 

[robinbanks]

For the stud walls that already have 100mm insulation board I assume that's as good as it's gonna get? Or can I add some roll over the top of this for even more thermal performance?

For my money, with your place as it is and if I had a pile of insulation boards and tools of wool sat on the driveway I would:

* clear all that wiring out of the way temporarily including moving that socket - bashing a hole in insulation just so one can leave a "held on by one screw" socket in place is awful attention to detail
* fit wool insulation between the studs that lack it (wool is easier and faster to fit than board and doesn't need as much fiddling at the edges as board does, because it can be cut slightly larger and squeezed into place, whereas board is cut smaller and foamed into place)
* fit board insulation over the tops of the studs, and foam and tape the edges, with channels cut out for pipework etc; the back side of that stud wall should look like one long sheet of celotex, and it should extend up between the rafters and connect to the ceiling board too
* take the ceiling boards down, fit a VCL and Insulation boards, then put the ceiling back up .. or vcl and board over the existing ceiling with insulation backed board

 

[GeddyMortgage]

Really thanks for the breakdown and advice again @robinbanks, and apologies in the late reply, we were away for the Christmas period.


On my return I've already took your sound advice and had the ceiling improved by adding insulation backed board over the existing ceiling, thats helped. The temperature in the rooms, albeit losing a bit of space in them, i feel it was a worthy trade-off.

Below are the next things I want to address, with a couple questions


Focus Area 1:- Insulating the poorly insulated / uninsulated walls that seperate the bedrooms/bathroom from the cold loft space surrounding them (as mentioned on previous post)

Question 1:- There's actually 2 areas here that are an issue (i've added the birds eye view again for reference). Firstly there's the boiler room on the right , there's no insulation in the stud wall that separates this room from the adjoining bedroom.....And as if that wasn't bad enough, as well as this, there's no insulation whatsoever between the boiler room and the loft space surrounding it, the only thing separating the boiler room from the loft space is some plywood that the boiler is attached to etc... (not hugely known for its thermal properties thin plywood eh)... I think I already know the answer to this question.... but i should just throw caution to the wind and insulate both these areas? Basically entire insulate the boiler room....meaning there'd be 2 lots of insulated walls between the loft space and that bedroom then...where there currently is no insulation in the walls separating them...

Question 2:- I can only fit in 50mm of thermal board in the stud wall that separates the boiler room and bedroom as the studs arent very deep. Is there anything stopping me deepening the voids by adding more timber to those studs, essentially increasing the depth of the stud, allowing me to get 100mm of insulation board in oppose to the original 50mm? and if i do, is it worth it?

Question 3:- The double doors between the boiler room and bedroom are only 35mm thick pine doors. My plan was to hang a floor length curtain behind them, entirely enveloping them on the boiler room side to further help the cold stay out of the bedroom.... Is this the best way of dealing with these thin french doors from a thermal perspective...and again.... is it worth it?



Focus Area 2 :- The insulation on the loft floor is no where near regulation. Where it's been 'boarded' the boards are directly atop of the 100mm joists with only 100mm of the old glass wool type insulation beneath, the none boarded areas have 150mm or so insulation which is very untidily laid... and worst of all... there are some large areas of that loft floor which are completely uninsulated where I can see very large areas of the plasterboard of the master bedroom ceiling below......(i've tried to show this on the attached birds eye diagram)

Question 1:- I've read online, if you want to increase the amount of insulation for the boarded areas, the best way to deal with this is install new timbers 90degrees to the current 100mm joists, lay insulation in those new channels atop the current insulation, then board over the top. I know regulation is 270mm-300mm. Im not sure i'll be able to raise it that high due to the layout of the loft structure and the position of the beams. But, even if I only lift it to 220mm in total, it's still worth doing, right (compared to the current 100mm)... In which case the timbers i'd need to buy would be 120mm by 45mm or so?

Question 2 :- As we've got vented eaves I wanted to ask about the areas of the loft that I dont plan to board. They too only have 100-150mm insulation currently. If I want to top that up to say 300mm (no boarding) with regards to the edge of the property where the cavity walls and eaves are.... how far from the 'edge' should I go with the insulation? I know It cant block the flow of the vented eaves....but typically how far should it go? Im concerned that if I dont go 'far enough' it's going to leave an easy route for the drafts from the vented eaves to get in...entirely circumnavigating the £100s/£1000s of insulation im looking to put in.

Question 3 :-For the loft floor areas im not boarding but do want more insulation on, is it still sensible to lay and rollout the 'top up' insulation 90degrees off the original 100mm insulation? or does it not matter?



thanks again and sorry for such a long post, the house is still struggling to stay warm despite all the work we've done on the ground floor insulating it.... I strongly believe now the problem is to do with the cold vented loft space and someone's very poor effort to insulate it thereof.

 

[robinbanks]

FA1 - Q1,2,3 bring the boiler into the warm envelope of the house by insulting all round the walls of the boiler room on the loft side, with board or wool between studs and board over studs. This helps protect pipework against low temps. Don't bother insulating the wall between bedroom and boiler cupboard. Insulate all dark blue areas with 300mm of loft roll, 100 between ceiling joists and 200 over at 90 degrees

Wood has some insulating value but not as good as insulation. Do not deepen studs to put more insulation between them; studs are for wall structure and structure is fine, as it's not falling down so doesn't need more stud, just more insulation. Insulating over the top of studs helps

FA2 Q1 - use loft legs rather than continuous timbers. Add more wool insulation to come up to 300mm

Q2 lay wool out to the eaves, leaving a gap of 2 inches cut/pluck wool ends so it chamfers down ie fit the max amount of wool that gives 2 inches down the eaves

Q3 roll at 90 degrees if you can, or well fitted no gaps above joists if you can't. Remember, cover wood with insulation where possible.

 

[GeddyMortgage]

Thanks @robinbanks

I've updated the birds-eye view as I've realised the floorplan I took it from was actually really inaccurate.

FA1 - Q1,2,3 - Let me share a video with you below....it's difficult to explain well the situation with words and birds-eye plans, i think i can implement everything you said, just have some questions on the video about some of the quirkier bits. Sorry it's a little long!

Focus Area 1 Video (Boiler Room Insulation)

FA2 - Q1,2 - Again ill share a video below, as would love some advice on the areas that look to me to be difficult / impossible to access! Wondering the best plan of attack.


Focus Area 2 Video (Loft Floor Insulation Difficult Areas)


Again sorry they're a little long! Very quirky house! and thanks again!

Ged

 

[robinbanks]

Just watched video 1.. Aye carumba, there are some complete spanners out there in the building industry. That celotex wedged in 30% of the rafters has a draft above it, a draft below it and in some places a gap down the side of it you can get your finger in. It's doing naff all to insulate anything and would be as effective if you took it all out and stood it up in the garden

Given the amount of pipework etc that you've got around the place I wouldn't bother trying to insulate any vertical or horizontal surfaces in that room; take all the insulation out of it and instead use it (and add to it) to insulate the roof slope and turn it into a warm roof construction, sealing the eaves up and bringing the boiler and all the pipework into the warm envelope of the house. I'd wool between the rafters, board over them and tape the joints to provide a VCL. As is, all that pipework is effectively outside; how you didn't get a frozen burst in the recent cold snap I don't know, but lucky you didn't cos the house underneath would be trashed if you did

Still amazed at the laughable job done by the builders. We've got no chance at meeting greenhouse gas emissions targets in this country if the housing stock continues to be put together like that!

 

[robinbanks]

Taken a look at video 2 and again, because of the complexity of what you've got in terms of tiny spaces and lots of services etc running in them uninsulated, I think the best route is to convert the house to having a warm roof and then everything is inside the envelope. It's tricky with the limited access and genuinely, I think the easiest approach might be to take the roof off in stages and do the conversion from the outside, or to pull those dwarf walls out and put em back later.. A perhaps slightly unorthodox approach would be to fill these small spaces with blown-in xps beads..

What is the final roof covering? Slates? Concrete tile?

 

[GeddyMortgage]

Aye carumba indeed, unfortunately that isn't the end of the shoddy workmanship im afraid, I found more stuff today where insulation in the roof/dorma is entirely being bypassed because of huge gaps between where the vertical celotex boards are meeting the angled ones in the roof, we're talking like 200mm gaps in some cases. Beggars belief that this was signed off, my house has an EPC of B!!!! I'd rate it closer to an F or G! Shocking.... i'll share a video of this shortly as had some questions about that, may be pointless in light of your last suggestion of going for a warm roof type. Couple questions on that.

:-So I understand you right, you're talking about on the otherside of the boiler room right? The loft space with all the insulation down. You're suggesting I dont try to insulate the vertical surfaces on the other side of that plywood that holds the boiler in place (or anything inside the boiler room infact). But instead remove all the insulation and put it up in the rafters instead, then seal the eaves. Right?

:- Is there a good reason why anyone would've opted not to do that in the first place? Why would some one knowingly go for a cold roof setup like this given the choice? I've asked a few people over the past month about just blocking up the eaves to stop the drafts but all I hear back is no no, they keep the rafters and trusses dry with the airflow they let in. If I block them up won't I get issues with damp and moisture etc?

Also if I remove all the insulation off the loft floor wont that just be killing some of the thermal protection regardless of whether it goes in the rafters or not? cant I leave the loft floor stuff as is AND wool the rafters too?

btw This evening before I saw your reply, I went ahead and lagged almost all the 22mm pipes before running out of lagging.....Haven't had the heating on the see the difference...yet.

 

[GeddyMortgage]

It's tricky with the limited access and genuinely, I think the easiest approach might be to take the roof off in stages and do the conversion from the outside, or to pull those dwarf walls out and put em back later.. A perhaps slightly unorthodox approach would be to fill these small spaces with blown-in xps beads..

What is the final roof covering? Slates? Concrete tile?

I'd considered having that stud dwarf wall out and get insulation in that way, wife is fine with this (it's her office). Blown in XPS beads i've heard mixed things about them and the power cables being buried by them.

Roof is Rosemary clay tiles.

 

[robinbanks]

Roof is Rosemary clay tiles.

I was afraid you were going to say that..