Victorian house DIY loft insulation

newfoundglory

I’m DIY insulating the loft of my Victorian house from c1900.

Its not a big loft, and the loft was only about 50% insulated to the 100mm between the joists when i moved in earlier this year. What was there was old and squashed, yellow itchy stuff, so out came the old and in went the new Eko Roll from Knauf. 100mm between the joists.

The loft is noticeably colder but 100mm is, apparently, still inadequate for today’s standards! Yes, the weather has turned and is a bit chilly (but Victorian houses are meant to be cold and draughty, right?)

I would like some storage space, but installing a raised loft storage floor might not make sense, because its already too low for a loft conversion. What should I do?

Raised floor and more fake wool - will this cause condensation/damp/rot?
Would insulation boards over joists work instead - but what and how thick?

Any thoughts appreciated.

Raxiel

Like you, I had patchy 100mm insulation between the joists with boards over the top. When we had a combi boiler installed I took the opportunity to top it up to the recommended 300mm, what I did was to remove the existing boards, remove what filthy and disintegrating insulation was present then install a couple of hundred loft legs from B&Q (there are others at other DIY stores, but the B&Q ones came to exactly 300mm above the bottom of the joists, and had plastic clips that gripped the joist and allowed easy installation.


Then Insulation was installed between the legs and the original boards replaced. I also had to build up the loft hatch to attach the ladder.


He'res a picture of what it looked like part way through.



The already cramped loft has 200mm less headroom but it's still adequate for basic storage, which is all it was good for in the first place. Its hard to quantify exactly how much benefit topping the insulation was, but it was a definite improvement and worth the time I spent on it.


It was not an easy job though, requiring several long evenings of working in dirty cramped conditions, and I had to pilot drill and then fix several hundred screws, so it's not to be taken lightly. More recently I did my parent's loft, and I was glad that after showing them how to do it over the first 1/3 of their loft, my brother and dad did the rest themselves.



It is possible to get insulated loft boards you can lay across the joists and walk on, as well as laying a sandwich of MDF Celotex and more MDF but they can be quite expensive.


Damp shouldn't be an issue provided any vents along the ridge line of the roof are left open, and you don't shove the additional rockwool right in between the rafters, leave a couple of inches for airflow up from the eaves. If you want to be extra sure, you can buy roof felt vents online for a couple of quid each, with a dozen or so enough to do a typical roof (I put one in every other rafter on both sides). They work by separating the felt at an overlap point, to allow airflow from under the tiles.

matelodave

I also used loft legs - have a look on Youtube to see how to install them.

The cheapest place I found them were Wickes at £10 for 12. B&Q want £15 for 12 and Screw fix want £19 for 12 so it's well worth shopping around as you need quite a lot of them.

If you want to use insulation board then you'll have to overboard it as it wont be strong enough to support stuff and it works out to be very expensive.

As Raxiel says make sure you don't block up any ventilation to avoid condensation.

We've got 140 sq.m of loft space which is insulated to about 350mm but only about 30sq.m is boarded over

Mutton_Geoff

The old stuff, and the dust it contains is very hazardous to your health. I'd leave it where is was. Use new stuff to top up to joist top level if need be then go across the whole lot at right angles with new 200mm insulation.


Leave the eaves clear for ventilation and a small space for storage if required. Make sure water tanks and pipes are lagged and DO NOT insulate under the tanks, let the warmth escaping from below keep the tanks from freezing but do lag the sides and top of the tanks well. Better still, go for unvented system and get rid of all water from the loft.

Cardew

Mutton_Geoff wrote: »

The old stuff, and the dust it contains is very hazardous to your health. I'd leave it where is was. Use new stuff to top up to joist top level if need be then go across the whole lot at right angles with new 200mm insulation.

Agreed - that's exactly what I did - laid 300mm on top of existing 100mm.

Raxiel

matelodave wrote: »

I also used loft legs - have a look on Youtube to see how to install them.

The cheapest place I found them were Wickes at £10 for 12. B&Q want £15 for 12 and Screw fix want £19 for 12 so it's well worth shopping around as you need quite a lot of them.

If you want to use insulation board then you'll have to overboard it as it wont be strong enough to support stuff and it works out to be very expensive.

As Raxiel says make sure you don't block up any ventilation to avoid condensation.

We've got 140 sq.m of loft space which is insulated to about 350mm but only about 30sq.m is boarded over

The thing to bear in mind with the Wickes legs is they are about 30mm shorter than the B&Q legs, and they won't stand up by themselves until you have at least one screw in. That doesn't make them bad, but I prefer the B&Q despite the extra cost. They have their uses though, in my parents loft, it wasn't possible to slip the loft ladder under the (horizontal) collar tie with the full 300mm so we had a section on the Wickes legs that was slightly lower and had a small step around it. Like so.



Wickes legs have a smaller footprint, which makes them easier to fit into tight spots. Along the edges and around things like the chimney and various timbers I had to take the jigsaw to the head of a few B&Q legs.



You also might find the odd joist that's deeper than all the others, a row of Wickes legs between the B&Q legs can even that out too.



Thinking back, I was wrong in my first post when I said I had 100mm, ours was closer to 50mm joists with 30-40mm insulation (where there even was any, most had none at all), so we needed the extra height to get the full 300mm.

Mutton_Geoff wrote: »

The old stuff, and the dust it contains is very hazardous to your health. I'd leave it where is was. Use new stuff to top up to joist top level if need be then go across the whole lot at right angles with new 200mm insulation.


Leave the eaves clear for ventilation and a small space for storage if required. Make sure water tanks and pipes are lagged and DO NOT insulate under the tanks, let the warmth escaping from below keep the tanks from freezing but do lag the sides and top of the tanks well. Better still, go for unvented system and get rid of all water from the loft.

That is sensible advice.
I wanted mine gone so I could fully inspect the roof structure & lighting circuit, as well as get rid of sixty years worth of birds nests, wasps nests & dead animals up there. That required the full on paper suit, goggles, gloves, and appropriate dust mask (not those cheapy decorators ones). I had to bag it up in the loft with the hatch closed. Filthy job (most of the filth on the insulation was actually tar that had flaked off the felt above it), I was glad when it was over & wouldn't recommend it unless you need to see what's under it.



Parent's loft was just a top-over job.