Loft insulation - what do I need?

breaking_free

Hi forumites.

My 3 bed bungalow has 250 mm yellow fibreglass loft insulation in the new-build extension. The original house though, the loft insulation is pink, thin and crumbling, so needs total removal and replacement. I want to do this myself but I'm overwhelmed by information on the Internet and now my brain is boggling. For example, the recommendation for fibreglass is 250 (I think), but rolls only seems to come in thicknesses of 200 or less (yes I know I could double up thinner rolls but I'd like to just roll the stuff out once). 

I've read that rockwool is superior to fibreglass but pricier. I'm okay with that, but again I'm getting overwhelmed by the choices available so thought I'd just turn to you people and ask for advice. I found this site here - not very obvious clickable link - which seems pretty comprehensive, but I don't know if this is the best place to buy it.

The total area is 118 metres square, but as the new extension is already insulated I probably need half of that. so 60 to 70 square metres.
So the questions are, what do I buy and where do I buy it?

Thanks all.

tacpot12

You need some insulation to go between the rafters. The nominal thickness of this should ideally be the depth of the rafters, but you could go a little thicker, e.g. 100mm if the rafters ar 75mm. 

You then need to more insulation across the rafters and the insulation that is between the rafters. This insulation should take the total insulation above 270mm (so it will normally be about 200mm). 

The main advantage of rockwool is that it is incombustible. If your bungalow is not detached, but has a fire resisting partition wall between adjacent properties, I would recommend going with the Knauf Space Blanket (200mm) product over the joists as this is very easy to handle as a DIY'er because it is encapsulated in a silver plastic foil that reflects heat back into the house. e.g.  Knauf Space Blanket Loft insulation roll, (L)4m (W)1.14m (T)200mm | DIY at B&Q

You can use the Rockwool 100mm RollBatt loft rolls between the rafters. Some suppliers will have these rolls in pre-cut versions that are either 400mm wide or 600mm wide, but if your rafters are spaced at different (or variable) widths) you can buy them without the pre-cutting. The rolls can be cut to the required width with a saw - you need to do this with the plastic packaging still around the roll!  You might need to call the supplier to ensure you are getting the correct width or not pre-cut. 

If you are very keen on the fire-resistance on Rockwool, you will need to buy 200mm Rockwool rolls to go over the  rafters, e.g.  Rockwool Thermal Insulation Roll - 100/200mm | Wickes.co.uk  

Look to see if any of the online retailers can beat the Wickes/B&Q prices, but check that VAT is included, and don't forget to factor in delivery. If you need more than you can fit into your can in couple of trips, have a look at hourly van rentals to see if this is cheaper than getting the insulation delivered. 

breaking_free

My bungalow is fully detached 

Wow, £55 for a roll with 3.32 metres square coverage. So I would need about 20 rolls of this stuff at a total cost of £1100. Does this seem about right for the job? 

WustyRex

bungalows have big floor plans and therefor big lofts .
Shop around, try eBay and Facebook marketplace.
Try ALL the builders merchants and also all of the alternatives to fibreglass. 

FreeBear

breaking_free said: Wow, £55 for a roll with 3.32 metres square coverage. So I would need about 20 rolls of this stuff at a total cost of £1100. Does this seem about right for the job? 

https://www.wickes.co.uk/Knauf-Insulation-Super-Top-Up-200mm-Loft-Roll---5-61m²/p/109451 - Only £25 per roll. There is little difference in thermal performance between rockwool and fibreglass insulation. They are both non-combustible, so won't burn in the event of a fire. Shop around and the likes of B&Q and Wickes often do a "buy 2 get one free" or similar discounts.

Grab a few rolls of 100mm to lay between the ceiling joists, and use the 200mm laid at right angles to ensure full coverage.

breaking_free

This is terrific advice. Thanks everyone. 

Eldi_Dos

With Easter coming up and the start of the DIY season for many,there can be good offers available that weekend.