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Hemp insulation in loft and loftlegs

humblebee hive – retrofit #1

It’s fair to say phase 1 of humblebee HQ’s retrofit has stretched over quite some time…

We started planning – with a duly filled-in draft Passivhaus (PHPP) model – back in, ooh, I don’t quite recall, but a good 2.5-3 years ago. We are broadly aiming for the EnerPHit standard (Passivhaus for Retrofit).

Insulating the loft

As reported in my last news update, we have started with the basics: loft insulation, though even that wasn’t straightforward. I’d imagined unrolling lightweight rolls of wool insulation over smooth-ish ceiling boards, between joists and then in the opposite direction over the top without so much as breaking a sweat – simples, I thought… how wrong I was!

Having decided to primarily use hemp in the loft as a super-rapid renewable, UK-grown resource, the fleece only came in batts that were a certain size, which, when we measured between the joists, I wasn’t convinced would be a snug enough fit, so we ended up ordering two types of insulation, 100mm thick woodfibre batts that friction-fit between joists and another 200mm’s (2x100mm) worth of HempFleece batts, which would eventually need cutting to size, as a quick plan sketch of the loft would suggest, but also fitting to structural elements. The most effective tool for that was a saw.

Then there was the decision to board a small area for storage – with 2 growing children, and nephews that could potentially inherit hand-me-downs, we were keen to keep hold of things without having them take up space in what could be seen as a compact house (in “extension-town” where we live, it certainly is compact).

Boarding requires “loft legs” – I wanted to find wooden ones but failed, and so got the proprietary (eponymous) recycled plastic ones, of which there are only two or three sizes, and not all in the same place – we eventually settled with 300mm tall ones to make sure we had a ventilation gap. It’s worth searching preloved sites as many seem to end up on there, though I could only find the smaller type second-hand.

Getting OSB boards (the “right”, environmentally OK kind) and the right size legs from the same shop required a bit of online hunting and needed another calculation / sketch diagram to work out quantities (how many legs per board etc.?).

This area eventually doubled as we realised our stuff – even after a massive cull – was getting too much for the 12 boards we’d originally ordered.

We also realised the area above the bathroom had recessed light fittings with messy cabling, a disused water tank, a gas pipe that made its way above the joists and across to the boiler in the landing cupboard – we eventually found out it was no issue to cover it up, but overthinking is my speciality (it’s not pipe-in-pipe so does it need ventilating? should we wait until we’ve decommissioned the gas? do we-redirect the pipe? etc.).

After a mildly panicky post to Carbon Coop’s retrofit assessors, Richard advised us to buy protector hoods, also by “LoftLegs” – these are still in their boxes, waiting for a day where we can face tidying up the area above the bathroom, and silicone the hoods in place for airtightness. And probably once we have ducting installed for the ventilation system.

hole in ceiling
A Flo-shaped hole

Then there was the mildly comical episode of “mum’s fallen through the roof” as exclaimed by our daughter while on a dance zoom call (this was in the early days of lockdown after all). My OH could only laugh as I disappeared through a Flo-shaped hole in my daughter’s ceiling, landed on her bed, rolled off and bashed my shin against a chair, but luckily broke my fall enough not to warrant a trip to hospital. Which wouldn’t have been fun – only ironic, considering we’d spent most of the first lockdown telling the kids not to “run with that knife” or not “bounce off the sofas” because we certainly were “not taking you to A&E”!!!

Moral: if you watch YouTube videos months in advance, make sure you refresh your viewing just before you start. I’d obviously forgotten the part about putting a plank down between joists to move around the loft floor!

We’re about to embark on phase 2 and the loft is nearly all insulated, and the central part nearly all boarded: still have the above-bathroom area to do and the loft hatch to sort out.

Costs #1

24 Boards (8 x 3No) and 72 (6 boxes) LoftLegs £115.20, VAT £28.80 (Total £144.00)

Hemp Thermafleece insulation £1,454.00, Steico-Flex Woodfibre insulation £540, Delivery £135.00, VAT £425.88 (Total £2,555.28)

Labour: DIY (loads and loads of hours/weekends)

Bruised ego, priceless.

Total loft (to date) £2,700 for 56.5m2 (£47.80/m2 loft area, or £23.90/m2 GIFA). Corrected 2/3/22

Target U-value: 0.126 W/m2K

Comments (6)

  • Interesting to hear you have used hemp thermafleece. We wanted to insulate the ceiling in the cellar (under the kitchen floor) and we found a type of sheep’s wool insulation that is made in Ireland. It was really easy to use (no nasty prickly bits or smell). We think it has made a difference! but the best bit really was how absolutely simple it as to install.

    • Both hemp and woodfibre lovely to work with. We didn’t really need the mask gloves or glasses in the end. That was more about moving old mineral wool insulation out of the way. The biggest H&S risk turned out to be my (lack of) wits: forgetting NOT to kneel on ceiling boards when getting back up on your feet 😂.

  • Great to read about the starting point of your EnerPHit Florence. I’m also over-thinking a retrofit currently, and also starting with the obvious stuff, windows just been upgraded and doing the loft by topping up with hemp, alongside roof replacement soon. We’re not targeting EnerPHit, but I’ll do my best to get it as low as possible. I’m interested to know how you’ve detailed the eaves with your additional insulation?

    • Thanks Kate. I have a preliminary eaves detail sketched by one of my architect collaborators but yet to be fully worked out with the EWI. As soon as I have the final version I will share on here.

  • Fantastic, Florence you had me laughing at the ‘mummy’s fallen through the ceiling’ bit. It happens!
    You will so not regret the experience, material or the cost In money or ego or time.
    I’ve a cathedraled ceiling- wood fibre sarking, loads of sheeps wool more wood fibre and lime hemp render and a clay paint – so good!
    So looking forward to the next post.

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