Adding 200mm fibreglass insulation to existing 30 year old 100ml insulation

[Prosper]

I'd very much appreciate advice on any possible future problems I could cause by adding 200mm fibreglass insulation to existing 30 year old 100ml insulation (which has sagged a bit so now not 100ml) and how the risk of these possible problems might be reduced.

My house is a 30 year old terraced 2 bed townhouse. The original insulation is of a yellow coloured layer (I assume fibreglass but not sure) between the joists. I'm adding 100ml fibreglass "wool" between the joists and then I'll roll out another 100ml layer across the joists.
The roofing felt above is that brown cardboardy type with a rough mesh type texture to it, and I've no idea how breathable it is.

My concern is condensation.

I've bought loft vents to shove down at the eaves so that air from the eaves can still get into the attic while pushing the additional 200ml of insulation as far as I can to the eaves.

I'm conscious of the fact that the access hatch up to the attic is from the bathroom and also that there are LED 3 downlighters in the bathroom. This means that moist air is more likely to travel up to the attic.

 

[Buddyboy]

Hi Prosper,
I did a similar job a few years ago - added between the joists and across the joists. You will certainly notice a difference in the heat retention of the house. Since you are wisely putting in loft vents, you should not have condensation issues, and since you are not doing anything to the rafters (e.g. stapling sheet insulation) then they should not be affected.

As you have LEDs in the downlighters, you won't have to worry about heat, as you would with halogen. What I would do is put three clay flower pots, upturned, over them in the attic, and insulate around/over them. Also I assume you have an extractor fan in the bathroom, that exhausts to the outside. Make sure of this, as otherwise all the steam will go into the attic - that is not good. If you don't have one, now is the time to fit one, when you are in the attic.

Regarding the access hatch, insulate above it, and use draught excluders (the small rubber strips) to ensure it is sealed when in the closed position.

 

[Prosper]

Since you are wisely putting in loft vents, you should not have condensation issues

I got the loft eaves vents in SIG Ireland off Turnpike Road. €25 for a pack of 10. They're very thin plastic and only about 300mm wide but I think they'll do the job.

What I would do is put three clay flower pots, upturned, over them in the attic, and insulate around/over them.

Although I changed from halogen lamps to LEDs for safety reasons as well as running costs, I still would like to put a cover over them and was going to check out today where to get the hoods. Clay flower pots are a great idea - thanks for that!!

Also I assume you have an extractor fan in the bathroom, that exhausts to the outside.

Yes I do have an extractor fan in bathroom that exhausts through flexible tube and out through the roof and it's the only outlet for moist air as no windows in bathroom. I must check to see if I can put a time-out on the fan as I'd be afraid now with all the insulation that it could overheat if I forget to turn the lights off in the morning (fan is activated by light switch)

Regarding the access hatch, insulate above it, and use draught excluders

I bought foam insulation strip draught excluder yesterday and I'll stick polystyrene whiteboard to both sides of the hatch and then stick some of the loft insulation on it also.

 

[Buddyboy]

Hi Prosper,
You're not me by any chance?
I have done/would do exactly what you are doing.
I used the same eaves vents, and because the pitch of my roof was so low, I slid in some 4" piping to ensure there would be a path for the ventilation (and not be blocked by the insulation. You may not need to do this.
And I wouldn't worry about the fan overheating. They are cooled by the air blowing through them. I think, but stand to be corrected, that you can't time-out the fan if it is powered by the light switch. Once the light is on, then power is going to the fan. You can get ones that time out a set number of minutes after the light is turned off.
And while you're up in the attic, make sure the extractor flexible pipe isn't, or cant, hang down anywhere, as if it fills up with water, then it will act like a U-bend in a sink and stop extracting.

 

[Prosper]

You can get ones that time out a set number of minutes after the light is turned off.
And while you're up in the attic, make sure the extractor flexible pipe isn't, or cant, hang down anywhere, as if it fills up with water, then it will act like a U-bend in a sink and stop extracting.

Yes it times out after the light is switched off. The flexible pipe is not taut and so coils around a bit on the floor before heading up. I hadn't thought that was an issue but now that you've mentioned it, it seems logical that moisture would gather and eventually block the passage of air. I'll see if I can fix it. Heading back up to the attic now so I'll have a look. Thanks.

 

[Leo]

Wrap insulation around the hose from the extractor too. That will greatly reduce the levels of condensation forming within the hose around this time of year when the attic space is cold.

 

[Foobar]

@Prosper @Leo I was up in the attic today doing a quick survey as the house is freezing and I'm going to give this a go next week. I am in similar situation as you, and I have a couple of questions.

Firstly, where did you go for all the materials?

Insulation is missing in places and 50mm (found old some insulation bags up there that said 2") everywhere else. I would need to top up the 50 to 100m, but I am considering dumping it and putting down new 100. I don't think it's possible to buy 50mm roll. The other option would be to fold / move the existing insulation so that it's doubled-up and then buying about half the amount of 100 to cover the remaining.

What did you do regarding the wiring for the lights? Did you just insulate over them?

And the last thing is that the width of the joists is about 320mm - I see most rolls are preforated to 380m, should I trim the excess?

 

[Tomo225]

One quick point do not put ceramic flower pots over the spot lights it is a fire hazard as they will absorb the heat, have seen this been done and d cables and spots have melted almost causing a fire , from an electrician,

 

[Foobar]

@Tomo225 Thanks. I have no intention of doing that as there are no spot lights fitted. Just ordinary lighting - should I insulate over or under the wires?

 

[Jazz01]

Foobar - you should put in around 12 inches of insulation. Within the joists, then at right angles across the joists. All wiring should be on top of the insulation - don't bury the wires under it.

Woodies DIY are doing good offer at the moment in relation to insulation... €15 for a roll of 200mm - not too sure of the length, but it's a good price. You might be able to get a discount from a co-op etc, if bulk buying rolls of insulation.

 

[Leo]

You can get 1.2m rolls that you can cut down to 320mm, that'll probably work out cheaper than trimming 380mm rolls. Proper builders providers are usually best, shop around online then call your local providers for a price keeping in mind they'll likely quote exclusive of VAT.

Measure the depth of the joints and get insulation of that thickness. Cut that to 320mm widths and fit in place. Perpendicular to that, roll out another layer to provide full coverage. 100mm in total isn't enough, aim for double this or even 300mm.

If you want to create some floor space for storage, you could place pre-insulated boards such as these above the joists.

Ideally cables should go above the insulation.

 

[Foobar]

Foobar - you should put in around 12 inches of insulation. Within the joists, then at right angles across the joists. All wiring should be on top of the insulation - don't bury the wires under it.

Woodies DIY are doing good offer at the moment in relation to insulation... €15 for a roll of 200mm - not too sure of the length, but it's a good price. You might be able to get a discount from a co-op etc, if bulk buying rolls of insulation.

You can get 1.2m rolls that you can cut down to 320mm, that'll probably work out cheaper than trimming 380mm rolls. Proper builders providers are usually best, shop around online then call your local providers for a price keeping in mind they'll likely quote exclusive of VAT.

Measure the depth of the joints and get insulation of that thickness. Cut that to 320mm widths and fit in place. Perpendicular to that, roll out another layer to provide full coverage. 100mm in total isn't enough, aim for double this or even 300mm.

If you want to create some floor space for storage, you could place pre-insulated boards such as these above the joists.

Ideally cables should go above the insulation.

Thanks. I have kept the insulation away from the eaves, but is it ok to insulate all the way to the boundary wall with the neighbours house? i.e. For a semi-detached house, the side of the house which is attached.

 

[Leo]

Thanks. I have kept the insulation away from the eaves, but is it ok to insulate all the way to the boundary wall with the neighbours house?

Absolutely, yes.

 

[Foobar]

Ideally cables should go above the insulation.

What to do with shower cable as it enters the ceiling?

 

[Prosper]

Hi Foobar,

Insulation is missing in places and 50mm (found old some insulation bags up there that said 2") everywhere else. I would need to top up the 50 to 100m, but I am considering dumping it and putting down new 100. I don't think it's possible to buy 50mm roll. The other option would be to fold / move the existing insulation so that it's doubled-up and then buying about half the amount of 100 to cover the remaining.

Work slow up there and take care. If your phone or doorbell rings then don't rush down to answer. Wear a good dust mask, hat and get a light with headstrap. Have some timber to place across joists to allow you to move about. I used some shelving planks for this and these allowed me to slide along on my belly to insert the eave vents and to ensure the insulation went as close to the edge as possible. Bring, a large scissors, stanley knife, duct tape, masking tape, electrical tape, pipe insulation tubing, staple gun (I used this to staple the eave vents to the soffit) and a small hand-held cordless vacuum cleaner up with you.
Your old insulation looks identical to mine. Don't remove it or move it about too much as you suggested you might in your posts. Where there's no insulation just place some new insulation cut to suit the bare spot. When all the bare spots are done, roll out 100mm new insulation in same direction as the old. Try to keep any electric wires above the insulation where possible. Then lay a second 100mm layer across the joists. You might find that it's now difficult to keep all electric cables above the insulation, so wherever it's covered mark the spot with some masking tape - I didn't do this nor did I mark the places where wiring comes up through the ceilingboard but I think it's a good idea.
Cover all pipes with foam tubing. You'll probably find that they are wrapped with some of the old insulation - what I did in this case was to wrap some larger diameter tubing around this and used a lot of masking tape to wrap tightly around that - no gaps.
Get a lagging jacket with lid for the cold water tank (got mine in SIG Ireland - also got the eave vents there). Wrap the tank with the jacket and tie it (1/3 from top & 1/3 from bottom) with the ties provided but leave some slack i.e. no too tight. When you're running your second layer of new insulation up to the tank, continue it up the side of the tank and tuck it into the two ties to hold it in place. Also, because I suffer from Perfectionitis, I used aeroboard (Woodies) to seal the area under the platform that the tank rests on. This is not really needed because I had run the insulation up the sides of the tank but I wanted to really ensure that I totally sealed off the un-insulated area under the tank from the rest of the attic in order to absolutely minimise heat loss up into the attic.
While you're up there it's a good time to create some storage space. In my small attic the only place to put up shelving was on the wall furthest from the attic hatch. I laid attic flooring (woodies) across to the far wall from the hatch and put shelving that could hold heavy loads into the block wall. Half the flooring had to be raised up to meet the other half of the flooring and I used "Loft-Lifter" (Woodies) for this. I bought a battery power drill/driver (1/2 price in Woodies) for safety and take care to ensure no wires get trapped between floorboard and joist. Don't use any of the roof timbers to support shelving or at least not to support anything that will be heavy.
I took some photos but I don't know how to get them into AAM

 

[Prosper]