boarding and insulating a loft - support and ventilation

Hi group,

Advice / experience / "I've done that and this worked" suggestions much appreciated!

I want to board my loft for storage, and insulate under (not between) the rafters so that things don't get too cold or got up there.

Currently it has a few boards thrown down (old wardrobe fronts!), with

5cm vintage glass-fibre insulation between the rafters, and 20cm 2006 glass fibre insulation on top of, and across, that.

I'm concerned about loads, and ventilation after insulation. Here's the details...

=== description ===

1973 terrace house. Loft.

Ridge parallel with front of house (i.e. running left/right full length of house). No hip in roof.

Party wall to right, old external wall to left.

=== current woodwork ===

  1. joists running front to back (sitting on inner cavity walls) are 11cm x 5cm. spacing (centres) = 41cm. Span = 714cm, covered by two 397cm long joists overlapped by 80cm and nailed together.

  1. Then there are three cross-beams 10cm x 5cm, running left to right sitting immediately above these joists, nailed to each and every one of them. Span = 572cm plus ends sitting in party + old external wall.

  2. collar ties running front/back (15cm x 5cm)

4.

2 very chunky beams running left/right (30cm x 5cm) supporting rafters mid-way up

5.

1 flimsey wind-brace

6.

7.5cm x 5cm rafters (41cm spacing).

7.

15cm x 2cm ridge

=== "problems" ===

== 1. support

The joists aren't supported from below (apart from the cavity walls at each end, 714cm apart!). All first floor walls are stud partitions and don't offer any support. The joists aren't that beefy.

So I worry that boards + lots of things stored on top will be too much for the existing joists.

It looks like the 3 cross-beams are supposed to be helping the 11x5cm joists to stay up, though some of the nails joining cross-beams to joists have simply split the wood.

Would screwing these existing joints, and adding another couple of similar cross-beams (have to be formed of two bits of timber overlapped and joined in the middle, since there's no way to get 5m of wood into the loft!), help matters?

If I do this, shall I run floor boards on the joists, or the cross beams, or add extra wood over, or in parallel to, the joists but attached to the cross beams, to carry the floor boards?

== 2. ventilation.

50cm Celotex under the rafters looks like the way to go. It seems there's a little ventilation at the eaves, but absolutely no ventilation at the ridge. How can I rectify this (cheaply, simply)? As long as I have good ventilation at eaves + ridge, leaving a well- ventilated "cold roof" above the celotex, I should be OK? Or should I have some ventilation directly into the warm loft space too?

Any advice greatly appreciated. While this space is "just" for storage, we don't have a garage, so it's the likely place that all kinds of things will end up - tools, toys+books+clothes (when one kids outgrows them and the other isn't ready for them yet) etc etc so it needs to be strong, dry, not too cold/warm, and fairly easily and comfortably accessible (so I have a decent loft ladder in mind, and all glass-fibre insulation will be banished, except below whatever floorboards I fit).

TIA.

Cheers, David.

Reply to
David Robinson
Loading thread data ...

[snip long description]

Would a photo be better?!

David.

Reply to
David Robinson

xxx

why not let things get hot and cold up there? a lot easier to insulate under the storage, less area than the triangular roof so less heatloss, and you keep lots of ventilation in the roofspace in case of damp.

that's what i'm going to do...

you only have to insulate at slate level if you're making a living space, and that means all sorts of fire escape regulations kicking in

Reply to
george [dicegeorge]

Because I don't want to. When _I_ go up there to get things, _I_ don't want to be hot or cold. I certainly don't want to be bringing cold thing down into the house (causing condensation on them). I want it to be as convenient as putting things away in a cupboard.

True, though the really easy way leaves a cold bridge.

They'll be some insulation below the new floor, as well as that just below the rafters. So it _could_ be made to have far _less_ heatloss overall, though I doubt I'll bother.

I've no intention of making a living space.

Thanks for the advice to not do what I want to do, but I still want to do it! ;)

Cheers, David.

Reply to
David Robinson

I'm with you David.

Stuff gets stored in lofts, and it's nice if the stuff is valuable in any way, that it doesn't get subjected to hot/cold/damp cycles.

I'm treating the loft voids in my house the same (4 corners around a dormer. Although it *is* more difficult, I'd rather have the roof insulated right into the voids as a) better for storage, b) there are many openings from the room into the voids and there's bound to be a transfer of moisture into cold spaces, short of sealing all the hatchways.

Reply to
Tim Watts

What did you do for ventilation above insulation?

Someone suggested Lapvents, but they seem a bit expensive.

Cheers, David.

Reply to
David Robinson

When I mentioned Lapvents, noone had heard of them.

Reply to
Tim Watts

So what did you use Tim?

I'm also looking at adding extra cross supports hung off the end walls, basically lifting the joists via screws from above - adding another two 100x50mm beams to the three already up there like this.

(It'll have to be two or three parts bolted together to get the 5.8m span.)

Do you think these will work...

formatting link

Reply to
David Robinson

I haven't yet. But upon removing some plasterboard and discovering that the two dormer roofs were well interconnected re ventilation, I decided to put generous fascia venting in both fascias, one vent per inter-rafter space. Winds should ensure a continuous flow over the dormer roof insulation and assist in drawing air from below.

My two remaining problems are:

a) How to vent uPVC fascias (not soffits, there aren't any) in a rain/sno proof way. Did discuss this last year here. Louvred gas vents seem to be the way others do it - I suspect the gutter offers enough natural shielding to discourage rain ingress.

b) How to interlink all the lower voids from the soffits on the main roof (down one level), allowing air up through the dormer walls and into the dormer roof space whilst still installing loads of celotex. Messy problem that. Probably will involve loosing a few inches from the room space.

formatting link
> Cheers,

Reply to
Tim Watts

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.