Loft boarding project

[bagstone]

Hello there,

Recently bought a house, and after finishing garden and everything else, the loft is now the "final" project. Did a bunch of reading up, but still have quite a lot of questions... here's a picture of what it looks like:

- The current joists are 100 80mm high. I read everywhere that 270mm total insulation is required. But we don't lose much heat in the house at all, and I plan to put insulation up on the sides between the rafters as well and then put boards on all sides as well, to turn it into a nice room (not with planning application, but just so we can put a mattress up there just in case we need a bit of extra space). Can I get away with just putting 100mm high beam on top or do I really need to increase it by 170? With boards and flooring on top it would raise it by 20cm which would just make the space very tiny, I probably can't even fully stand there anymore then. Plus I don't want to put 170mm high beams up since the weight would just be insane, and adding 70mm (or 100mm) spacers everywhere just seems dumb (and expensive and overkill).
- When I go to local building suppliers I find so many types of wood. So many acronyms (not a native speaker here so still getting used to all the British abbreviations, especially in the DIY scene). What type of beams should I buy? My plan was to get something like those here.
- It's a mid terrace house, and there's one solid wall (as can be seen on the left in the pic where the brick work goes up) at 3.75/2.75 from either wall. So my plan was to get 11 beams of 4.20m and 11 of 3m, cut them to 3.80 and 2.80 respectively, and then bring them up (all have to go through a narrow staircase and a newly installed loft hatch. Every 60cm, one end over the wall, the other attached to the wall using these truss hangers - they say timber to timber in the description but I can't find anything more fitting, are they okay?
- We're not sure yet what kind of flooring we'll put up there - we did some easy laminate downstairs which we really liked, so could envision that, or some carpets. Either way, taking some underlay and the flooring into account, is another reason we kind of aren't keen on going up the 270mm insulation madness, but also made us wonder what the easiest/cheapest flooring solution is. Thinking of something like this maybe, if my maths is right we'd need about 33 of those. Price wouldn't be too bad I guess, especially since Huws Gray always knocks off a lot on site compared to the price seen online. But a bit worried of the weight, as this chipboard seems quite heavy? Is that chipboard a decent choice or any other/better flooring solution? I like Huws Gray because they deliver super fast and are around the corner here.

Can post more details if I missed anything, but any tips welcome, also links to "must see loft boarding guides" though there's a good chance I've already read/watched them. Note that I did some loft boarding years ago, but different country/regulations so it's all a bit of a brain re-wiring for me, and easy to get lost in translation. Boarding is just the first step - then comes putting up insulation and boards on the sides, but I might make a new thread for that in a few weeks... especially regarding ventilation which seems to be the biggest thing I need to worry about before I just put something up on the rafters.

 

[cdbe]

I was out at the bit about putting a mattress up there.

 

[bagstone]

I was out at the bit about putting a mattress up there.

Well, that was just to say that in the long run I *might* want to use it for more than storage space. It's something the missus suggested, and it's to highlight that after flooring I want to make it proper nice and tidy, but for now just floor boards to clean it up as it's obviously quite messy.

 

[JohnD]

What are the dimensions of the joists, and their longest unsupported span?

Your roof has a breathable membrane, so it will keep fairly clean. This would be a good time to buy or hire a builders canister vacuum cleaner, and clean out all the old dust, also any old yellow fibreglass fibres, if present. The modern mineral wool treated with Ecose does not shed irritant dust and fibres. Do not use a domestic vac.

If you have any old fibreglass in there, wear a mask until you have bagged it up, removed it and vacuumed. Do not carry it through the house unbagged.

I would advise treating the timber against woodworm, and especially Longhorn Beetle if you are in Surrey.

 

[bagstone]

What are the dimensions of the joists, and their longest unsupported span?

They're 4x2 joists, so 100mmx50mm. Unsupported span... hard to tell, I didn't take the fibreglass up since I didn't want to create a mess. But I guess just judging by the dimensions of the walls on the first floor I assume it's the length of the rooms below, so roughly 4 meters.

Your roof has a breathable membrane, so it will keep fairly clean.

Yeah I think the roof was done about 10ish years ago (we don't know for sure, it was done before the previous owners so at least 4 years ago, but a neighbour said around 10ish years ago). Just to be clear when you say "will keep fairly clean" - once boarding is done, I want to put insulation between the rafters and put up boards/cladding on the rafters to make it into a nicer space.

This would be a good time to buy or hire a builders canister vacuum cleaner, and clean out all the old dust, also any old yellow fibreglass fibres, if present.

That's a good shout, I was thinking if I should do that. I asked my dad if I should remove all the rockwool and he advised against it - to be fair, it doesn't look too bad, probably also not much more than 5 years old, it's not just put in between the joists but there's a layer of paper/cardboard to contain it. So my thought was to not take it out... especially since I either need like 50 small bags and 10 trips to the tip, or a skip (which the Mrs hates as it means no parking for 3 weeks). And the dust and added money for new and so on. But... there is some dirt on top of it which seems prudent to leave on before boarding the loft. Hmmm.

I would advise treating the timber against woodworm, and especially Longhorn Beetle if you are in Surrey.

Ah, I'm just back from Huws Gray looking at beams, asking about whether people buy treated or untreated they said they sell both for loft boarding - but it sounds that treated might be desirable in that case? We're not in Surrey but Northwest, never heard of beetle issues here to be fair.

 

[JohnD]

That's a good shout, I was thinking if I should do that. I asked my dad if I should remove all the rockwool and he advised against it - to be fair, it doesn't look too bad, probably also not much more than 5 years old

What colour is it (under the dirt)? Show us close up pic

I can tell by feeling it. I don't know if you will be able to tell the difference by feel.

The safer stuff is soft and fluffy with a slippery feel.

 

[bagstone]

What colour is it (under the dirt)? Show us close up pic

I can tell by feeling it. I don't know if you will be able to tell the difference by feel.

The safer stuff is soft and fluffy with a slippery feel.

Ah well. I think it's much older and worse than I thought. I pulled a bit back and took some close up shots. Looking at it like that I think the safer bet would be... wear some old clothes and mask, bag it all up, and clean it all... sigh. Here's an album with pics:

https://imgur.com/a/f9ua7rV

Also re-measured the joists, they're 50x80mm, not 50x100mm. 40cm in between then. Not sure what I measured that I thought it's 100mm.... will edit first post as well.

 

[JohnD]

Looks like yellow fibreglass.

 

[Dereekoo]

Well at 4m span and 50 x80 those joists will just support a ceiling load of skimmed plasterboard and keep allowable deflection in permissible limits and be ok structurally. Adding chipboard would mean deflection would exceed permissible limits but would still be structurally sound, Start adding other loading up there and things get interesting. Having said that, if you add chipboard and screw/glue it down to the joists then the joists start acting as Tee beams with greater loading capacity but to what extent???. I did something similar to my loft 30+ years ago as a sleepover den for the kids and mates (don't tell cdbe) and except for a few hairline cracks in the ceiling it served its purpose (span was about 3m) kids now gone and loft floor now has 300 depth of insulation on top. Don't know what prospective buyers will think when it gets sold with a boarded out plastered loft with access by pull down loft ladder but that will be the kids problem to sort.

 

[bagstone]

Well my plan is definitely not to put the load entirely just on the existing joists - I'm putting beams in that go over the load-bearing wall on one side and are attached with hangers to the side walls of the house.

Just did some more reading up and discussed with the Mrs and it sounds like we definitely want to go for the 270mm insulation (urgh) to not lessen the value in case of resale and a prospective survey, which means I either need to get 8x2 beams (which I think would be too heavy) or 4x2 or 6x2 beams and then add 50mm or 100mm spacers throughout (which would be a lot of spacers and a lot of faffing around). Neither solution particularly appealing but better do it right than a half-assed job that bites us in the ass when it comes to reselling...

 

[bagstone]

Okay, did some more reading. Apparently loft legs are out of the question as they're not meant in between joists but directly underneath the chipboard, and not good for walking, only for storage lofts. So not really what I want.

Which means I need to get either the 8x2 beams. Or... find some other way to raise the new beams above the old beams to get the 270mm. Or... one thing I can't figure out despite using the forum search and Google and what not - can the 270mm insulation be spread between loft ceiling and rafters? Since I intend to put insulation between the rafters anyways before I board the sides, doesn't that add up to the rest?

 

[JohnD]

Consider first that the loft is not suitable to be a habitable space. So making a structural floor and boarding the rafters will be wasted expense. It will not add value to the house unless you do a proper loft conversion with a staircase, fire protection and Building Regulations approval.

If you want to use it for light storage and occasional walking, you can create a central pathway by laying additional timbers down the middle, at right angles to the existing joists and screwed down tightly. This will add rigidity and spread the load to reduce the risk of ceiling cracking. It will become even more rigid if you floor with a ply deck, screwed tightly down. Ply is stronger than chipboard, and I think lighter.

 

[bagstone]

We're aware it might not be a superb "habitable space", like it's not going to be a room we enter every few days or even weeks. But maybe once a year when the extended family visits for a weekend the kids can sleep up there on a mattress. Or I can put up a small workshop in the corner, and maybe some gym equipment. That's the plan, besides storage. The loft isn't too high (2.5m at its peak) but it's good enough for us to be wanting to board it - we have no desire to put in a proper staircase or get planning permission though. Also, the loft has 2 very good Velux skylights, they seem to have been added just a few years ago as they look as good as new. So there's already natural light. All we need to do is board the floor and rafters to make it look a bit more nicely.

 

[JohnD]

"Superb" is not relevant

Either it's a habitable space, or it isn't.

Yours isn't.

Sorry.

 

[bagstone]

I'm a bit confused what makes you say that, could you elaborate? Other people in this street with exactly the same houses have bedrooms in the loft as well and did what we're planning to do (we viewed other houses in this street prior to purchase). We're aware that this is not going to be a room we can advertise on Rightmove, it's not what we intend to do...