Insulating loft floor. unfelted roof (Ed.)

[Greggle123]

Hi all,

First time posting so bare with. We've just got a new place and the survey suggested that we add some insulation to the floor of the roof. It's an old house c.250 years old and amazingly the roof is sound, maybe a few tiles need replacing but as I'm aware no leaks.

The loft space has insulation between the floor joists but is very patchy, dusty and looks bad. There's gaps where downligths where installed later. So I'm thinking of the following and just checking a few things / worries I had.

- remove old insulation
- put loft lids on the down lights to prevent any gaps (there are many)
- place 100mm insulation between joists
- install some loft legs on one side for a few boxes to go on
- lay 170mm going the other way to the joists

Is this correct? Should I be worried that an unfelted roof may allow water to get in and then cause mold on insulation?

Should I be putting insulation all the way up to where the pitched roof starts?

Am I right to say I shouldn't put any kind of waterproofing stapled to the pitched roof battons?

Many thanks!

 

[JohnD]

Yes, that will work. If the roof is unfelted, there will be constant dirt and grit entering, but not as bad as in the days of open fires and factory chimneys. If you want the loft to stay clean you can add a barrier under the tiles, such as roofers breathable membrane stapled to the rafters. I don't know if this is really worthwhile. I recommend a foam gun and pink expanding fire foam to seal holes around pipes and cables (wrap the cables and fittings and allow future access to junctions boxes and connections)

You must leave open eaves ventilation to prevent condensation and damp. You can get eaves ventilation channel to prevent the insulation blocking them.

If the old insulation is yellow fibreglass, I strongly recommend wearing a mask, hat and goggles while you bag it up and clean the loft with a builder's canister vac (not a domestic vac) fitted with a filter as well as a bag. Dirty yellow fibreglass sheds irritant dust and fibres. I have a chest condition and it is quite severe for me. It could be bad for anyone prone to asthma.

Modern brown mineral wool treated with Ecose (marked on the packaging) does not shed irritant dust and fibres.

Loft legs are OK, though I prefer putting additional timbers at right-angles to the existing joists and screwing them down tight. Drill pilot holes at a skew, alternate sides, near the foot of the timbers or you will need enormous screws. This spreads the weight and adds rigidity to the deck, even more if you screw a ply floor to it. Do not use a hammer and nails or the ceilings will fall down. I use decking timbers which are quite cheap.

If you have L&P ceilings that are cracked or the nibs broken, I can explain how to reinforce them before they fall down.

 

[JohnD]

See also https://www.diynot.com/diy/threads/...ng-laths-with-metal-lath.613440/#post-5512576

 

[Greggle123]

Yes, that will work. If the roof is unfelted, there will be constant dirt and grit entering, but not as bad as in the days of open fires and factory chimneys. If you want the loft to stay clean you can add a barrier under the tiles, such as roofers breathable membrane stapled to the rafters. I don't know if this is really worthwhile. I recommend a foam gun and pink expanding fire foam to seal holes around pipes and cables (wrap the cables and fittings and allow future access to junctions boxes and connections)

You must leave open eaves ventilation to prevent condensation and damp. You can get eaves ventilation channel to prevent the insulation blocking them.

If the old insulation is yellow fibreglass, I strongly recommend wearing a mask, hat and goggles while you bag it up and clean the loft with a builder's canister vac (not a domestic vac) fitted with a filter as well as a bag. Dirty yellow fibreglass sheds irritant dust and fibres. I have a chest condition and it is quite severe for me. It could be bad for anyone prone to asthma.

Modern brown mineral wool treated with Ecose (marked on the packaging) does not shed irritant dust and fibres.

Loft legs are OK, though I prefer putting additional timbers at right-angles to the existing joists and screwing them down tight. Drill pilot holes at a skew, alternate sides, near the foot of the timbers or you will need enormous screws. This spreads the weight and adds rigidity to the deck, even more if you screw a ply floor to it. Do not use a hammer and nails or the ceilings will fall down. I use decking timbers which are quite cheap.

If you have L&P ceilings that are cracked or the nibs broken, I can explain how to reinforce them before they fall down.

Thanks for the response John, really appreciate it! Will have a look tomorrow to see if there are any pipes or cables I need to seal. I don't really mind about the dust as things will be in plastic boxes for storage or can cover with a sheet. So if it's not necessary to prevent any rain coming in then I'll leave it.

Do you have a link to eaves ventilation? Not sure what product I should use.

You're right about the old insulation it's the yellow itchey stuff. Can I hire a builders vacuum rather than shell out for one?

Good idea about not using loft legs. They are rather expensive. I guess the draw is that insulation can be cut and placed over them before mounting a board? But does that really make a difference?

Would you use something like this for the timber?

4.8m C24 Sawn Green Treated Timber Decking Joist 47mm x 100mm

C24 Sawn Green Treated Timber Decking Joist 47mm x 100mm Measuring 47mm wide and 100mm high these decking joists are High Pressure treated with Tanalith 'E' and graded to C24 for known structural performance, these timbers are perfect for use as a supporting frame to your composite decking...

www.cladcodecking.co.uk

We do have a L&p ceeling so would appreciate advice on making safe before I crawl around up there and end up in the kids bedrooms

 

[JohnD]

Timber looks OK

Link added above for ceiling

You can buy a canister vac quite cheaply. Aldi and Lidl occasionally have them. Cheap brand at Screwfix is Titan. Wet and dry can also suck out drains, or wet carpets, overflow from bath or the pit for a stopcock

https://www.screwfix.com/c/auto-cleaning/wet-dry-vacuums/cat810212?sort_by=price

Always ensure you can buy filters and bags to fit before buying one. I think mine is 30 litres. Very useful in workshop for wood dust and shavings, can be attached to some saws and planers. Quite noisy.

 

[JohnD]

Example ventilators

The relative humidity of a correctly ventilated loft space should be similar to that of the outside air.

If an RH of 54% in the loft isn't great, what is the RH you are aiming for in the living space, and what is it currently?

Refurbishment Rafter Tray 480mm x 350mm - Eaves Ventilation | Roofing Ventilation

Buy Refurbishment Rafter Tray 480mm x 350mm Harcon RR46 Online. The Harcon Range of Eaves Ventilation Systems are Available for Fast Nationwide Delivery From Roofing Ventilation.

www.roofingventilation.co.uk