Attic Insulation - Max Possible with Floorboards?

gaelicyoda

Hi All,

Got a bit of a pickle here (for all us non-construction types anyway), which hopefully someone can help me figure out.

I'm looking at a new shell of a house at the moment, and the person who built it has been considerate enough to make it easier to convert the attic space by having engineered steel purlins used to support the roof load - please see my very crude MS Word 5-minute-special attachment.

Since I wouldn't be in a position to convert the attic space immediately, my initial plan was to have 400mm fibreglass in the attic space - 2 x 200mm rolls, one layer on top of the other, with each layer rolled perpendicular to the other (i.e. the bottom layer between the joists, with the other on top "lenghtwise"). I would also be putting a 50mm laminate kingspan board instead of plain plasterboard as the first floor ceiling.

However, I've since come to realise that I will probably need some attic space for storage, etc. and that if I actually want to floor the attic, I'm going to have to come up with something else.

All I can see that I can do with it really is put 100mm rafterloc between the joists (leaving a 50mm ventilation gap, and using insulation tape to seal the insulation to the timber, and the breaks between insulation sections) and then screw in the attic floorboards to the joists on top. Same again for the rafters. To do otherwise would basically mean compressing the fiberglass to an unacceptable level, which would make a mess out of its effectiveness/efficiency.

Using this setup, if and when I do then come to convert the attic, I could unscrew some of the floorboards (the ones between areas "2" and "3") to reclaim the rafterloc - I assume they will become unnecessary at this location at this point, since any heat lost from downstairs will be permeating into a habitable area now - and put relocate it into the areas in the attachment marked "1", "2" (into the vertical section) and "3" (into the vertical section), and then screw the boards back down again.

Based on this "plan", can anyone tell me:

(1) Why you might be looking in disbelief at your screen right now shouting "NO, YOU %$@**!!!"? :mad:

(2) Following on from (1), any other ways of maximising the attic insulation between now and the time I do the conversion (whenever that may be - a number of years at least more than likely) in such a way that I can re-use as much of the insulation I put in now as possible to essentially wrap around the converted space?

(3) Anyone else have a similar situation in the past?

(4) What kind of percentage decrease (just roughly) in u-value I could expect between this setup and using the 400mm fiberglass, and indeed any suggestions made for (2) and the 400mm fiberglass setup if you can estimate it?

(5) A bit adjacent to the point, but which side of the rafterloc (in the rafter section) should an extra vapour barrier go, if any? From another post I read, the poster indicated that the rafterloc on it's own is not sufficient for this purpose. I'm guessing the extenal-facing side.

Cheers,
GY.

sydthebeat

gaelicyoda...

as you have many different questions in your post id suggest the following.

1. use the search function at the top of the page. you have asked aboout many issues that have been debated here many time over.

2. ask your professional. as this forum is NOT tpo be used as a substitute for professional advice, id suggest you should be running these questions by the professional you have hired to:
1. offer advice on compliance with building regs and planning permission
2. certify the remaining stages of teh build
3. produce your BER rating as is legally required


at the end of the day, no matter what is suggested here, your professional wil have the final call as to how they view compliance...

gaelicyoda

Hi Syd,

Fair enough - maybe it was what I was searching for initially, but took me ages to find something that would go some way to answering what I was trying to figure out.

For anyone reading this who's in the same boat, I came across this post (so hopefully I can save someone some time):
http://www.boards.ie/vbulletin/showthread.php?t=2055545861&highlight=attic+floor+insulation

Basically, the suggestion here is to put an extra layer of joists on to the existing ones to fit extra insulation, but obviously this would have head height implications.

I was kind of hoping really to get people's real life experiences with this issue - specifically, what they did and ultimately how it worked out for them.

Anyone feels like posting this kind of info here, please do.
(or indeed has a link to a post with some more relevant info?)

I take your point about the professional advice as well Syd, that will be the goal, but I just wanted to fore-arm with a bit of knowledge before any meeting takes place (as I said, I'm just looking at this house at the moment) so that we're on the same page from the get-go.

Cheers,
GY.

gizmo555

gaelicyoda wrote: »

Basically, the suggestion here is to put an extra layer of joists on to the existing ones to fit extra insulation, but obviously this would have head height implications.

I was kind of hoping really to get people's real life experiences with this issue - specifically, what they did and ultimately how it worked out for them.

This is exactly what I did in half of my attic. This is the start of the first winter since I installed the extra insulation, but so far so good. As I'm only using the space for storage, the head height is not an issue for me. The house is definitely a lot easier to heat and retains heat longer. Mind you, I also pumped the cavity, replaced the windows with much higher performance ones, and installed HRV so it's impossible to accurately separate out the real life contributions each improvement has made.

By the way, at the insulating contractor's suggestion, I laid the extra joists at right angles to the existing ones, as opposed to laying them straight along the top. The reason was to minimise cold bridging.

gaelicyoda

Thanks for that Gizmo, glad to hear it all went well. Good call on the perpendicular joists as well, makes good sense.

I would be using the space for storage initially, but ultimately I would be going for a full conversion. I'm in kind of two minds at the moment on how to go about it - I think I probably should just bite the bullet now, and prep the joists for taking the load of an attic conversion rather than the lighter load of partial storage (I don't rightly know what this would entail, maybe a few RSJs across the tops of the internal walls through the center of the house to stop ceiling sagging?). The obvious constraint here of course would be cost.

Having said that, I'd imagine that it would be far, far cheaper to do it now than to go off half cocked and have to tear up the attic floor later when the conversion is on the cards. Decisions, decisions ...

On pumping the cavity, had you already got some insulation in there?

gizmo555

gaelicyoda wrote: »

On pumping the cavity, had you already got some insulation in there?

Yes, the house was built in 2000 and is standard twin leaf block cavity wall, with 110mm cavity, of which 60mm (I think) was filled with Aeroboard-type rigid insulation.

This is fine as far as it goes, but as is often observed here, is only as good as the care with which the blocklayers installed it, especially around things like bay windows, of which I have two.

gaelicyoda

Thanks Gizmo.

Just to digress from the original topic for a moment, getting pumped bead insulation is an idea I've been considering myself. How do you handle service pipes/wires coming into and out of the house with respect to the insulation?

Is there some kind of ducting surrounded by expanding foam or something like that?

gizmo555

gaelicyoda wrote: »

Just to digress from the original topic for a moment, getting pumped bead insulation is an idea I've been considering myself. How do you handle service pipes/wires coming into and out of the house with respect to the insulation?

Is there some kind of ducting surrounded by expanding foam or something like that?

In my experience there was nothing to handle. There was no overspill of beads from the types of spot you mention.

gaelicyoda

Well, it was more the thermal aspects of the electric cables and hot water pipes I was getting at - the beaded insulation is not meant to come into contact with anything over about 70 degrees (if memory serves me right) so cables and pipes coming from outside in through the cavity wall (and indeed, vice versa) would have the potential to cause problems to the insulation

gizmo555

gaelicyoda wrote: »

Well, it was more the thermal aspects of the electric cables and hot water pipes I was getting at - the beaded insulation is not meant to come into contact with anything over about 70 degrees (if memory serves me right) so cables and pipes coming from outside in through the cavity wall (and indeed, vice versa) would have the potential to cause problems to the insulation

I'm open to correction, but I can't imagine what pipes or cables one might have coming in through the cavity which would come anywhere near this temperature.

gaelicyoda

I'm open to correction ...

Me too, absolutely I thought I had read in another post that special care should be taken with mains power cables and the like, but maybe I just interpreted it wrongly.

Anyway not to worry, I can check that out myself offline to see if I just misunderstood.

Thanks for the info about your experiences, much appreciated.

gizmo555

gizmo555 wrote: »

I'm open to correction, but I can't imagine what pipes or cables one might have coming in through the cavity which would come anywhere near this temperature.

Actually, now that I think of it, flues for stoves or boilers could well reach or exceed 70C.

I suppose the best thing to do is make sure the product you are considering has Irish Agrément Board certification, then download the product certificate from the NSAI website: http://www.nsai.ie/Our-Services/Certification/Agrement-Certification/Search-Agrements-Certificates.aspx

These certs contain detailed installation and recommended usage instructions which you can refer to. The cert for the product I used contains this paragraph, which may be the thing you had in mind in relation to power cables:

In cavities where electric cables can come into contact with expanded polystyrene, in accordance with good construction practice all PVC sheathed electric cables should be run through ducting.

gaelicyoda

In cavities where electric cables can come into contact with expanded polystyrene, in accordance with good construction practice all PVC sheathed electric cables should be run through ducting.

Yep, that's ringing some bells for me alright.

Zilog

I'm looking at flooring out the attic myself. I came across a product called 'Thermawalk' at one of the Self Build shows. Haven't purchased it myself yet and have no experience of this type of product.
Basically it seems to be a sandwich of insulation stuck onto chipboard. I see B&Q are selling it or a version of it also.
I don't know if it is suitable for high traffic areas, or if it's just intended for attic storage access.
Anyone use this type of product?

gaelicyoda

Hi Zilog, I came across this product as well, and I had a look on their website to check it out.

To me it looked more like it's used for maintenance walkways more so than either storage flooring or habitable area flooring, e.g. as a floor between the attic hatch and the water tank (in an attic without any other flooring) so that the plumber doesn't have to walk straight on top the joists.

I would be interested to hear as well though if anyone has actually used it