Eaves - soffit or what?

[Ed Davies]

An additional advantage of a warm roof (vs cold loft) is that it's much easier to make the insulation and airtightness layers continuous at the wall/roof junction.

[ToughButterCup]

1 hour ago, Patrick said:

OK. I thought I hold back on this topic since loads on here  are more clever then me. But maybe some readers here have a similar problem with the long explanations, just like me.

I always find a short YouTube video much more easy to understand than a 1/2 page written on the same topic. And sometimes I feel right stupid on here for not understanding a word, but then... Maybe some others are the same, so this might help understanding the ventilation issue :

[...]

 

@Patrick your post is one of the most helpful that I have seen.

It reinforces well understood research into  learning styles.  It would be brilliant if we could have someone whose job it was simply to search video resources to help those for whom a video, or an illustration helps more than  a screed of text.

 

It pains me to read that you are somehow to blame for not understanding written text. Let me be clear: you are not to blame. I spent many years teaching  teachers  (serving and trainee) to recognise that not everyone learns the same way.  It was an uphill job sometimes.

[Big Jimbo]

The above by Bouch is so true. If you gave my daughter a tractor manual and an evening, she would read it, and the next day without a manual, she would be able to strip the tractor, and rebuild it without any help. (I kid you not) I on the other hand would just rip it to bits, and then go and look for the manual.

[Stones]

56 minutes ago, Bitpipe said:

I guess its a different consideration for the volume house builder who is trying to squeeze every penny out of the build cost to maximise the profit and the self builder who had a different set of motivations.

 

Warm roof insulation, airtightness detail and MVHR are not standard volume house build elements and if they're not contributing towards creating a habitable space that can be marketed and be reflected in the house price (like a usable room in roof, which then implies windows, stairs, meets regs etc) then little reason to do it - unless there is downstream cost of cold roof construction such as a penalty or fine on the house builder. 

 

At a basic level, I would have thought that the lack of a fully functioning MVHR system is a large part of the problem - i.e. the continued reliance on trickle vents and extractor fans which householders keep closed / don't use? The installation of CO2 monitors to warn householders of poor air quality strikes me as a classic sticking plaster (perhaps due to industry pressure to avoid the significantly higher cost of MVHR).  All that warm moist air has to go somewhere , some/much of it ending up in the cold loft?  

[Bitpipe]

1 minute ago, Stones said:

 

At a basic level, I would have thought that the lack of a fully functioning MVHR system is a large part of the problem - i.e. the continued reliance on trickle vents and extractor fans which householders keep closed / don't use? The installation of CO2 monitors to warn householders of poor air quality strikes me as a classic sticking plaster (perhaps due to industry pressure to avoid the significantly higher cost of MVHR).  All that warm moist air has to go somewhere , some/much of it ending up in the cold loft?  

 

Agree - risk with a developer installed MVHR system is that a) it's installed poorly / not balanced and b) the home owner just does not look after it (cleaning / replacing filters, servicing the heat exchanger, correct settings etc).

[SteamyTea]

52 minutes ago, AnonymousBosch said:

It reinforces well understood research into  learning styles

https://en.wikipedia.org/wiki/Learning_styles

While doing my PGCE we had to try out all styles, but generally, we teach bet they way we learn.  Why some people just cannot learn from some teachers.

I wish English teacher could learn that.

[joe90]

12 minutes ago, Sensus said:

there is a significant extra cost involved in going from cold to warm roof construction,

 

As per my post above I disagree, depends on your definition of “significant “. With regard developers and costs I wonder if their customers would be interested in a usable loft as storage space within a warm roof as these houses are quite small and additional storage may be an advantage?

[willbish]

I fear i may be building a house that is susceptible to loft condensation.

Thanks for bringing the issue to my attention @Sensus, although I'm not sure what, if anything, can be done to minimise the potential issue. Fortunately I am currently building the roof structure so there may be time to make some changes.

I have to have a cold roof (loft) to accommodate a bat roost. The loft space will naturally be fairly air tight (ICF gables, OSB sarking on rafters) with one letterbox sized opening for the bat entrance.

The first floor ceiling insulation will be 300mm of spray foam under a 22mm P5 deck and between I-joists.

My ridge runs North to South and the house is in an exposed location on a ridge of high ground. With prevailing winds from SW

What is the likelihood I am creating a problem? I doubt there is a definitive way of finding out before I finish the build.


Possible ways I could alter course during the build:

-More letterbox openings, but as discussed more ventilation may not be the answer.
-MVHR input into loft space to warm the area. Would unbalancing the ventilation system compromise it's benefits.
-Insulate a small amount between the rafters to increase the temperature of the loft space

 

[joe90]

22 minutes ago, willbish said:

The first floor ceiling insulation will be 300mm of spray foam under a 22mm P5 deck and between I-joists.

 

I would imagine that with this amount and kind of insulation very little heat/moisture will escape into the loft space to create condensation.

 

are you creating a way of harvesting the guano ? ?

Edited November 20, 2019 by joe90
Add

[ProDave]

This is an interesting thread.

 

The present house is the first I have done with a warm roof.  I am absolutely 100% sold on the idea that a warm roof is the way to go for several reasons.

 

Our old house was "normal" cold roof and had 300mm of rockwool insulation in the loft.  For some reason I don't know, it never had any problems with condensation.  It had eaves and ridge vents and a couple in the gable ends as well. Never at any point have I seen any condensation.  The reason why I find that strange, is during my work I have been in many many similar looking lofts that have huge condensation problems and the inside of the sarking board is black with mould.

 

I wonder if the plasterboard is a significant contributor?  We used foil backed PB on the ceilings and all external walls. A lot of houses I see just use ordinary PB. And we didn't have any downlights (I used to hate them with a vengeance until LED lamps came along) so unlike many houses, no great holes in the ceiling to let moisture through.

 

But another HUGE plus for a warm roof is the total absence of rodents in the house.  The previous house had mice in the  loft every year. We were convinced they got in by climbing up the outside of the rendered walls and in through the sofit vents.  You have to have these vents so there is no way to stop mice getting in, so the only solution is to "deal with them" once they are in.  We have not had a single rodent in the new house because there is simply no way for them to get in.,

 

 

[willbish]

10 minutes ago, joe90 said:

 

I would imagine that with this amount and kind of insulation very little heat/moisture will escape into the loft space to create condensation.

 

are you creating a way of harvesting the guano ? ?

 

My (limited) understanding is that even without warm air leaking into the loft, condensation can form when naturally moist air inside the loft cools overnight and condenses on the cold loft floor.
 

The guano is the only benefit for having to house-share with bats! Guess we'll collect it just to stop it covering our attic junk

[Oz07]

I've never had a mouse in the loft to my knowledge, how would you know? I've never seen any signs although i'm sure they can climb walls - especially built by the brickies I use.

 

I'm going for the option sensus recommends on current place. Built it then deal with if it becomes a problem. Got fascia vents all around on a hipped roof, so the whole perimeter, vented ridge and a good area of roof south facing with no shading. Fingers crossed!

[Patrick]

@willbish

AFAIK , in  general it is often acceptable to have an outside bat rooster box. They call them bat bricks or something like that and it sits within the outer wall. Just if you want to get around this issue.

Edited November 20, 2019 by Patrick

[Jeremy Harris]

A development just up the road from us has internally fitted bat boxes, that are sealed from the main loft space.  There's a name for them (may be a trade name), I'll see if I can dig it out. 

 

 

 

[willbish]

5 minutes ago, Patrick said:

AFAI, in  general it is often acceptable to have an outside bat rooster box. They call them bat bricks or something like that and it sits within the outer wall. Just if you want to get around this issue.

I wish it was that simple, Im following a mitigation strategy proposed by an ecologist and approved by Natural England. Deviation could land me in the sh*t and not the good guano kind!

[Onoff]

45 minutes ago, ProDave said:

We were convinced they got in by climbing up the outside of the rendered walls and in through the sofit vents. 

 

You mean the brown or white round things where you drill a 70mm / 3" hole?

 

There were none here when we moved in but I found boxes of them in the stable. I felt a pillock when I went round with a 70mm Starrett then found they were 3". 

 

Still got one elevation to do...

 

I reckon here they come in through gaps in the footing bricks and up the cavity. Also through the crap detailing around the dormer cheeks.

 

 

[willbish]

Thanks @Jeremy Harris My loft space is designed for lesser horseshoe bats, one of the requirements is it must equal the volume of the roost that was lost when the old property on the site was demolished. 32m3 

[joe90]

50 minutes ago, willbish said:

Guess we'll collect it just to stop it covering our attic junk

 

Does that mean you have a loft hatch from the house up into the loft? As that could be difficult to seal and insulate. I had to provide ? bat boxes but our bat consultant allowed me to build them into my garage roof as I did not want to compromise our airtight warm roof. Mind the ecologist could not confirm what type of bat, but roosts were in small crevices which means they were not lesser horseshoe bats.

 

P.S. Planners still said I had to provide them in the house as well, but during our planning appeal the inspector said the council were not qualified to over rule the bat inspector ?

Edited November 20, 2019 by joe90

[willbish]

13 minutes ago, joe90 said:

Does that mean you have a loft hatch from the house up into the loft? As that could be difficult to seal and insulate.

Yep that's right. Im planning to use a passive type hatch with class 4 airtightness. U value is not too bad at 0.50 and I was thinking to install a PIR plug that would sit in the top to boost the insulation