Boarding rafters, need to worry about strength...?

[Magic Man]

With regards roof rafters, they are usually plasterboarded in loft conversions - is there ever a need to re-inforce them or are virtually all rafters easily capable of taking the weight of plasterboarding?

What about T&G cladding? In terms of weight per square metre, is 8mm T&G cladding lighter than plasterboard - my mind says yes but I'm not sure...

 

[big-all]

are you planing to complying with building regs!!!

are you talking underfoot or wall and roof!!

 

[noseall]

Boarding rafters or joists can actually benefit the structure by linking the whole thing together thus stiffening/tensioning etc.

 

[Magic Man]

Thanks for the replies. No building regs to comply with, just a loft storage room that I may house a computer in. Just would like something rather than the felt/sarkin (which can be dusty/dirty) above my head.

I was just wondering as to the weight of plasterboard that gets fixed up there when doing proper loft conversions. The floors get strengthened with additional joists but nothing for the roof rafters as far as I'm aware - and plasterboard is heavy.

 

[big-all]

well just remember light storage
use chip board flooring
just remember attics are bad places very damp - 20 to plus 60 very dusty
in general very hostile

 

[Magic Man]

Thanks. It is boarded - 5" joists, and is well ventilated (Velux window) and ridge vent. Will also have a dehumidifier up there in case of any condensation (although, no sign of any so far).

Will be putting a custom desk arrangement up there but that will be 'hung' off the purlins and wall mostly.

 

[big-all]

what length is the unsuported span off the joists as in between walls underneath!!
what is the spacing between the joists!!
these all relate to the loading abilit

 

[Magic Man]

what length is the unsuported span off the joists as in between walls underneath!!
what is the spacing between the joists!!
these all relate to the loading abilit

I'm not worried about the strenght of the joists. They're 5" deep, plenty capable of light use above - not going to be jumping up and down on them, just sitting on a chair at a desk. I'm not going to be putting anything of any real weight directly on the floor - desk surfaces will be off the wall and purlins with just bracing legs against floor.

Joists are roughly 44cm centres. Joists are nailed to ends of rafters and also to beams beneath the purlins (between beams is roughly 2m). There is an internal wall direct centre, at right angles to the joists - dual plasterboard, carboard honeycomb construction, not brick but capable of taking a slight deflection if there was any. There's a wacking great water tank sitting on a couple of joists that's been there for 30 years without any sign of deflection beneath (will be coming out next year).

From this...

To something like this...

 

[big-all]

so its cleary not a just a storage area!!
so i take it you are going to remain wholy unoficial and when you sell its still just a !"storage area" after you have spent a fortune on flooring insulation cladding when for about 50% more you can call it an incomplete loft conversion

 

[Chukka63]

roof spaces arent designed to take much weight so may find the ceiling sagging unless there are walls below supporting them.your plan looks quite detailed so im assuming ure insulating walls,ceilings???
ive just done a loft conversion and had to put a total depth of 160mm kingspan or similar to the walls.

 

[Magic Man]

so its cleary not a just a storage area!!

Yes it is. Storage for Christmas trimmings etc. in the side eaves, storage of computer stuff in the main part

so i take it you are going to remain wholy unoficial

Yep, nothing to be official about. It's my loft, it's not a habitable room, no difference really than putting the same stuff in a garage or a garden shed.

and when you sell its still just a !"storage area" after you have spent a fortune on flooring insulation cladding when for about 50% more you can call it an incomplete loft conversion

Nope. If we ever did sell then the desk stuff would be coming out and all that would be left would be panelling of the side eaves and loft boards.

Flooring cost less than £50, same for panelling. Haven't added any insulation other than what was down and don't intend to insulate the roof, just panelling to cut down on the draughts. It warms up pretty quick up there from body heat alone and PC stuff likes cool temps. A heater/dehumidifier will take the edge off any cold after 10 minutes if needed.

roof spaces arent designed to take much weight so may find the ceiling sagging unless there are walls below supporting them.your plan looks quite detailed so im assuming ure insulating walls,ceilings???
ive just done a loft conversion and had to put a total depth of 160mm kingspan or similar to the walls.

Granted, roof spaces aren't designed to take much weight but they will take a lot more than a lot of people give them credit for, especially older non-prefab/truss style builds. As said, I plan to hang any weight off the purlins and wall anyway, the only real weight on the floor will be me on a chair. After reading quite a few threads around here you'd believe your loft is ready to collapse if you put anything more than a Christmas tree and some baubles up there. People were storing shed loads of stuff in their attics before all the rules and regs were laid down and that was in older properties with 3" joists and lathe and plaster ceilings.

Nope, no insulation. Was brought up in the seventies/eighties in a house without central heating, no attic insulation and single pane sash windows. There was often ice on the inside of the glass upstairs in the winter and when I had my ZX Spectrum in the eighties I'd be sitting up in my room with a coat on and you could see your own breath.

It gets a little cold up there but it doesn't last. Everyone seems obsessed with putting down huge wads of insulation all around their houses and then wonders why they are getting ill and their attics are dripping with condensation. Open the front door once or twice in the day and the 'benefit' of all that insulation is swept clean out. I tend to live by the fact that I just accept some amount of heat loss from my home rather than trying to seal up every source of fresh air I can. Rather lose some heat than live in a sealed box.

 

[big-all]

sorry to seem a kill joy
i dont think you realise the extremes your attic will get to
in winter will be perhaps 5 degrees warmer than the grass temperature where as you unheated room will be around12 degrees warmer than the attic

with a 2.5kw heater blasting away with an outside temperature of say -6 and your attic at around -1 it will take 40 mins to raise the temperature to around 12 degrees

and in the summer if its 30 degrees in the shade it will be around 50 to 60 degrees in the attic a completly unbareable heat
just double the heat quoted in the shade on a sunny summer day to work out the attic temperature

 

[freddiemercurystwin]

it's not a habitable room

I largely agree with everything you've said except for this bit which is wholly incorrect an office is classed as habitable.

In defence of the advice given, you've been given good advice, people find it odd that you're going to the trouble of doing what you're doing when you could probably have a legal conversion for not much more £?

 

[Chukka63]

ignore advice at your peril.why come on here searching advice when you have all the answers?????.
is there no supports from the joists to the rafters,helping support the rafters????.and youre then loading the joists onto the rafters,thus adding more weight onto the rafters.if you get my drift.

 

[Magic Man]

Apologies if I seemed dismissive of the advice. I know and appreciate the advice given is correct and the best thing to do but a 'proper' conversion is simply not practicable and would certainly be a lot more than just a few £'s - unless you know anyone who'll do a 'legal' conversion for less than £500...? No?

I largely agree with everything you've said except for this bit which is wholly incorrect an office is classed as habitable.

Granted. But it's only 'habitable' if I say it is when looking to sell. It can be anything I want it to be whilst it's my property. As said, if we sold then there would just be boarding and panelling there, i.e. a storage space.

It's a small attic, the height to the bridge board is only 6' so there is no freespace to raise a floor. As said, the joists are attached to the hanging beams below the purlins and the distance between is 2 metres, there is a partition wall direct centre below and the joists themselves are 5" (more than capable of taking a fair amount of weight - certainly a single person sitting on a chair on boards that are screwed across three joists each, given that the same structure on the other side of the attic is holding a 50 gallon water tank - I weigh a fair bit less than 500lbs of static weight).

The purlins are 22cm x 7 cm and mounted into the walls with the roof rafters sitting on them roughly half way down, I'm fairly sure they are capable of supporting a couple of desk surfaces attached to them and the wall itself.

I appreciate the extremes of temperature. With all the wind yesterday, it was 10 degrees up there. Lowest I've recorded (on my trusty max/min thermometer over the years) has been 5. I do expect it to get colder next month and January but an extra layer and heater will take the chill off. In the summer it maxes out just below 30 (50 or 60? - this is Wales, not Dubai ) and that was before we had the window fitted (NE facing) and also before we discovered the ridge vent had been blocked up with insulation...

If it does get too hot/cold then I'll have to look at insulation between roof and panelling but I'll see how it goes first. There's plenty of free air movement up there so I'm not worried about condensation, no sign in over 13 years of living here, and the dehumidifer/heater is more than capable of dealing with any caused by me being up there.

I do appreciate the advice and my thanks for the replies, my original question was merely pondering over boarding rafters with relatively heavy plasterboard - it sort of moved on from there (original wasn't answered by the way ).