Putting insulation in attic

martineire

I'm goin to buy some rolls of insulation to put in my attic which already has insulation in it. I'm just wondering what thickness of insulation should I put into my attic? What is the best insulation on the market? And best value for money?

Thanks

Atlantic1

By far the best that's generally available is Moy Metac. Most professionals that I've come across in the business use Rockwool. Rockwool is fine but it is quite inferior to Metac. Metac has a thermal conductivity of 0.34. Rockwool is 0.44. And when you consider area per roll, Metac is very good value.

Google it and you'll get all the tech specs.

martineire

Good stuff ill use moy metac so. I'm just wondering I'm goin to put the insulation over my existing insulation or would it be better to take up the old stuff and put the moy metac between the joists? Or will I just simply put it on top of the old stuff?

I'm goin to lay the insulation between the joists would it be a good idea to also put it between the rising 45 degree rafters? Currently there is no insulation between them.

Thanks

Atlantic1

Some say to leave the old insulation. Personally, I would take it out and start from scratch with Metac. I did with my own attic. How deep are your joists? Put the exact thickness of Metac between them. DO NOT COMPRESS IT! It works best when expanded to its full thickness. Then cross lay another (and maybe thicker) layer over the joists. This will also prevent cold bridging through the joists and give you a very good u value, e.g., 2 x 100mm layers of Metac will give you about 0.17. Thicker layers will be better again.

There's no need to put it up along the rafters but do remember that the attic space above the insulation will be much colder now in winter so make sure that your tank and pipes up there are insulated/lagged.

And you should never put any insulation directly under the tank. The heat rising from below the tank will/should prevent it from freezing/bursting.

Good luck with it!

john_cappa

martineire wrote: »

Good stuff ill use moy metac so. I'm just wondering I'm goin to put the insulation over my existing insulation or would it be better to take up the old stuff and put the moy metac between the joists? Or will I just simply put it on top of the old stuff?

I'm goin to lay the insulation between the joists would it be a good idea to also put it between the rising 45 degree rafters? Currently there is no insulation between them.

Thanks

Keep the insulation in one place. Either along flat of joists or on the rafters.

No point taking up the the old stuff. It is still doing a job. Also no need to use the moy metac as it is pricey and the performance isnt that much better IMO. Yes it is slightly superior but if you use thicker cheaper stuff then its performance will be the same e.g

100 thick moy metac is 63.66 for 8.4m = 7.6 per metre


'earthwool' at 150mm thick (Will have same or even slightly better Uvalue that the moy) is 18.20 for 6.87 metres or 2.64 per meter.

So basically a third of the price.

(Also dont buy from that website as you will prob get a better deal in a merchants etc)

I would aim for 350-400 mm thick of standard loft wool.

BryanF

Atlantic1 wrote: »

Most professionals that I've come across in the business use Rockwool.

moy metac AFAIK doesnt have the same fire rating as rockwool

(mod hat on)
Atlantic1
please make your point without the bold text thanks

TonyToo

Hi,
did you complete your attic insulation?
the reason I ask is I'm am going to go the same. I will be adding insulation over the top of existing insulation that is already there between the joists. Did you lay the insulation over the electrical wires or did you lift the wires before laying it? I read somewhere that you aren't suppose to lay the insulation over the wires, i don't know what the reason for this was.

Thanks.

darragh_haven

john_cappa wrote: »

Keep the insulation in one place. Either along flat of joists or on the rafters.

Why does this need to be done? I have my insulation up along the rafters at the moment, but I'd like to add more on the ceilings over the bedrooms. Would it be wasted doing this?

rckfld

Also wondering what the situation is regarding laying additional insulation over wires.

I want to cross lay another layer of insulation, can I lay this over the wires?

lolosaur

in south dublin and looking for value on insulation. at the moment im looking at woodis on naas road, 30 quid for insulation with R value of 4.3 i think and then top up over it with r value of 2.97 (the one thats essentially wrapped in tinfoil)

Would i be better off looking for insulation from brookes/ tp smyths and doing it myself or getting a builder in to do it as they would probably get a trade price for the stuff.

also looking at that thermawrap tinfoil that you staple to the roof joists but its costly. Is it worth it. will it make a tap of difference.

BryanF

lolosaur wrote: »

in south dublin and looking for value on insulation. at the moment im looking at woodis on naas road, 30 quid for insulation with R value of 4.3 i think and then top up over it with r value of 2.97 (the one thats essentially wrapped in tinfoil)

Would i be better off looking for insulation from brookes/ tp smyths and doing it myself or getting a builder in to do it as they would probably get a trade price for the stuff.

also looking at that thermawrap tinfoil that you staple to the roof joists but its costly. Is it worth it. will it make a tap of difference.

In your case Stay away for foil backed insulation. If you place it above ceiling insulation ( on the cold side) it will just trap any moisture that escapes from the house below and make you insulation damp as regards the rafters are you heating the attic, if not, don't use it for similar reasons

rckfld

@BryanF with regards to my query, how should I go about placing additional insulation over my existing insulation. Can it go on top of the wires etc?

Thanks for the advice.

lolosaur

rckfld wrote: »

@BryanF with regards to my query, how should I go about placing additional insulation over my existing insulation. Can it go on top of the wires etc?

Thanks for the advice.

Ill ask you that one too bryan!


should i just go with the 4.3 and then a top up layer. whats the ideal? also, should i put rockwool over rockwool etc?

BryanF

rckfld wrote: »

@BryanF with regards to my query, how should I go about placing additional insulation over my existing insulation. Can it go on top of the wires etc?

Thanks for the advice.

I wouldn't like to say, im not familiar with your attic or wiring. In my attic I topped up with additional insulation and the earlier installed insulation was already covering the wiring.

declan52

the moy metac insulation contains formaldehyde so if it gets wet it will make your attic smell like cats piss. not nice. knauf do a high density roll that will stick between your rafters that has the same u value and is much cheaper.

lolosaur

best place to buy insulation?

in south dublin