Flooring a loft. Need some advice please.

Hi,

I am planning to board my loft mainly for light storage and an occasional quiet study area. It will mainly be used for storing cardboard boxes and fairly light weighing clutter. The study area will be a desk with a computer and a chair. This is not a loft conversion as the roof is not high enough and have nowhere to put a staircase. I just plan to board the floor and the rafters. So it will be more of a large storage cupboard accessed with a loft ladder. Most of the time, I will be the only one accessing the loft and I weigh 75 kilograms. The stored junk (spread across the two sloping sides of the roof) and study stuff will probably not exceed 100kg at the most. Then there is the existing cold water tank.

My house is a mid terrace which was built in 1926. It is of rafter and purlin style as seen in the pictures. The purlin isn't fixed to the brick wall, they are purely supported by three beams which are fixed to the ceiling joists at the bottom. The rafters are the same as the ceiling joists in both wood and size.

The ceiling joists are 4x2 and spans between the load bearing walls at the front and back of the house at 12" centres. There is also an additional load bearing wall more or less at the centre partitioning the font/back living room and master bedroom/hallway. There are also a few more non load bearing walls on the second floor which separates individual bedroom. Therefore there is some support at a few metres at the most. I don't know what wood the ceiling joist and rafters are made from, but they seem very solid. However warning from other people about the fact that ceiling joists cannot support a floor, I plan to install extra 4x2 joists (raising the floor by 2 inches) to cross batten existing ceiling joists at 12" centres to slightly strengthen the floor and to allow pipes and wires to remain undisturbed.

Due to various reasons, it is unfeasible to sister the existing ceiling joists, so I want to run additional joists at 90 degrees angle with a 3" screw at each existing ceiling joist. This framework of wood, will in theory, help spread the load to minimise floor deflection, but in practise, is this method good enough for strengthening the floor? If not what alternative do I have? Also are the rafters strong enough to support plasterboards? (They are currently supporting Marley concrete tiles which replaced natural slates).

I know loft boards and chipboard floorings are REALLY HEAVY! The last thing I want is for the ceiling joists to snap and the entire ceiling/roof structure to collapse! As this is my parent's house... the consequences are unthinkable! I would want to die if it happens. Can anyone advise me on what to do?

Overview of the loft.


The rafters- what wood are they? When cut, it has a sour smell.


The existing ceiling joists (4x2)


I intend to lay extra joists on top (similar to the ceiling tie beam) to support the floor. Each indicated by a blue line.
The purlins are supported by 3 support beams of which each one of them are held by three ceiling joists.

looking at your last photo with the blue lines, why not fit galvanised steel joist hangers into the mortar joint of the bricks on the front and rear walls, about the same height as the beam, fit new joists so that they finish slightly higher than beam and then lay t&G chipboard over, weight will be on the new joists rather than ceiling joists, this will also avoid sound transferring to ceiling below, especially if you fit foam joist caps

if your roof tiles are already concrete i suspect a surveyor would already be recommending some strengthening as concrete tiles are considerably heavier the original tiles that the rafters were designed to hold, unless you are intending re-tiling with lighter tiles i wouldn't recommend fixing plasterboard until a surveyor has assessed the load

an alternative would be to line with aluminium insulation http://www.wickes.co.uk/FOIL-INSULATION/Thermal-Insulation-Foil-Roll/invt/210022 and then screw 3mm plyboard over and paint white or if your budget allows you can buy decorative 3mm ply that they use in camper vans etc http://www.rainbowconversions.co.uk/Equipment/Boards/boards.htm

The reason why I don't want to make a suspended floor is because not only I have limited headroom (only about 8 inches at the highest pint), I don't want a bouncy floor at the center point. All I want to do is to cross batten and strengthen the ceiling joists to put down boards for storage without making the roof/ceiling collapse. Sound is not an issue as I wont be playing basketball up there.

Point taken for the plasterboards. I agree that it will be too much for the rafters to hold. Especially when it snows. I will use 3 or 4mm plywood instead after checking out their weights in my local timber yard. Tiles will not be changed as they were just replaced 4 weeks ago.

Thanks for telling me about the foil insulation. Do I just staple it onto the rafters and put plyboard immediately over it or do I need to put extra batten before putting in the plyboards? If the foils are good, I will get that instead of rafter rolls. Whilst we are on the subject, will condensation a problem for me?

I am coming round to the idea of WBP Ply for loft flooring rather than chipboard. it withstands moisture, and is stronger and lighter. It can be screwed down to the tinbers to fiorm a rigid deck. For light storage, 12mm WBP might be strong enough (but see if someone who really knows agrees).

I have used 9mm for loft shelving (nothing heavy) it is flexible until well-fixed.

Hi,

I am posting this message because I don't feel that my question has been fully answered yet. The questions that I would like answered are...

- How should I cross batten existing joists (type of timber required, spacing etc...)?

- Will cross battening reduce floor deflection and will the extra weight exerted by the timber/floorboards be safe for the ceiling/roof?

- Once I put the foil insulation on the rafters, can I board over it immediately or do I need another gap?

scartbix said:

- How should I cross batten existing joists (type of timber required, spacing etc...)?

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If it is just battened and you don't use adequately sized joists capable of spanning from party wall to party wall, it will achieve nothing.

Will cross battening reduce floor deflection and will the extra weight exerted by the timber/floorboards be safe for the ceiling/roof?

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As above. All it will do as battens plus deck will increase the loading to the already undersized joists (for domestic floor/light storage purposes) and actually increase the deflection of the existing ones.

If you really don't want to raise the floor level, you'd be better off putting a ply deck down, screwed to the top of the existing joists. But the boarding would have to run from wallplate to wallplate, only doing it where you want the useable space will be pointless. Screw centres will be v close at the supports, spreading out as you get towards the centre of the joist span.

I see Velux windows and I hear insulation, plasterboard and flooring.

you're trying to do a loft conversion without meeting building regulations, aren't you?

scartbix said:

The reason why I don't want to make a suspended floor is because not only I have limited headroom (only about 8 inches at the highest pint), I don't want a bouncy floor at the center point. All I want to do is to cross batten and strengthen the ceiling joists to put down boards for storage without making the roof/ceiling collapse. Sound is not an issue as I wont be playing basketball up there.

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I don't understand why you think joists will be 'bouncy' 4x2 joists fixed into joist hangers should be adequate for what you have described (1 person, a desk, and a few boxes)

Cross battening will only make the ceiling joists more rigid (less sideways movement) and is NOT increasing the load capacity of the ceiling joists - plus it is just adding more weight, something you were trying to avoid

As for headroom, you will always 'loose' the height at the edges but you will only loose about 5-6" overall if you lay the new joists so they sit 1" above the ceiling joist

Point taken for the plasterboards. I agree that it will be too much for the rafters to hold. Especially when it snows. I will use 3 or 4mm plywood instead after checking out their weights in my local timber yard. Tiles will not be changed as they were just replaced 4 weeks ago.

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Are you going to make the access big enough to get 2400 x 1200 sheets up there, if not you need to cut the ply down (will require extra joint capping and more work for you) you could consider lightweight cladding planks

Thanks for telling me about the foil insulation. Do I just staple it onto the rafters and put plyboard immediately over it or do I need to put extra batten before putting in the plyboards? If the foils are good, I will get that instead of rafter rolls. Whilst we are on the subject, will condensation a problem for me?

Click to expand...

I hadn't much experience of foil myself until I saw it in France in 2005 where it is very popular and widely used (much cheaper than over here too) they run it horizontally stapled across the rafters so you have an air gap between it and the roof tiles, starting at the top and working down, overlapping it by about 5cm with the next row down. As it is so thin they just screw plasterboard straight through it into the rafters

Thanks for your help guys. In the light of disappointing news about the strength of cross battening, I have decided to only board off a section of the loft (part of the eaves on both sides and around the hatch). 2x2 will be be layed to raise the floor slightly to allow cables to pass before laying panels on it (sheet material yet to be decided in the timber yard). They will need to be cut down to 600x2400 to fit through the hatch. Apart from where the boards will be, the rest of the loft will have the original amount of insulation (250mm) kept on it.

I would like to thank you guys for your time to help me in the past few days, I couldn't have decided without you. If anybody else has a different opinion, I would delighted to hear about it.

I see Velux windows and I hear insulation, plasterboard and flooring.

you're trying to do a loft conversion without meeting building regulations, aren't you?

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@JohnD. I am planning to do up the loft to make it more pleasant mainly for storage (plans have been changed now obviously), I am not building a loft conversion, I said this quite clearly in my opening post. The Velux window was put in as a replacement of the smaller old cast iron roof window which leaked. I wanted rafter insulation to compensate because I have to remove the top 100mm loft insulation to put the floor down. Not only is the roof isn't high enough for a loft conversion (RSJ and floor joists will need to be installed), the layout of the house means that there is nowhere to put the stairs without knocking down/cutting through walls- not something we want to do. There is no way I am going to do a loft conversion without meeting building regulations- its too risky. I am not going to compromise safety nor do I want to make the house unsaleable in the future.

In future, please think when implying about someone's work based on clues before pressing the submit button. Especially, think carefully how you decide to phrase it as it may offend someone.

Once again thanks for the advice guys!

If it helps my house has a room in the attic (probably converted 30 years ago) and all the floor joists are 4 x 2. They are 37mm apart so there's quite alot of them

lightweight cladding planks

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Has anyone more info on lightweight loft flooring?

Chris

WillB77 said:

If it helps my house has a room in the attic (probably converted 30 years ago) and all the floor joists are 4 x 2. They are 37mm apart so there's quite alot of them

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That is the exact size as mine. They look awfully strong and I was convinced that you can floor it with no problems until I did a detailed research.

I don't know why people say that you mustn't put anything heavy in the loft as the ceiling joists cannot support it... Obviously I know you must not put stuff weighing half a tonne up there but I find it hard to believe that 4x2 joists can only take so called "light storage" which is a light as a few empty card board boxes! It seems like that everybody thinks that ceiling joists are made from a few sheets of paper. I am sure that ceiling joists can take more than 2kg! If fact, most of us have a water tank up there which weighs between 200-300kg.

I tried searching on the internet for examples where ceilings have collapsed because of excessive loft load, but could not find anything conclusive. If ceiling joists really can't make more than a few kilos, then surely everybody's ceilings in the country will be collapsing left, right and centre!

I've not floored my loft yet but I will hopefully do it next summer.

On the last loft conversion I done, a previous owner had laid 4x2s across the existing joists to take a floor. The ceiling didn't collapse but it did sag, about 3in at the worst point.

You need to put the right size joists in.

The odd thing is that our 1930's semi has 3"x2" joists on the ground floor and there is a basement underneath !

The floor has a lot of bounce in it and I will be fitting a couple of 6"x2"s in each room to reduce some of the bounce, but that has held all the furniture for the ground floor for the last 70 years.

I think to be honest the calculations are based on worse case situations such as a pair of 48 stone Americans sitting in big heavy chairs. and lots of heavy furniture. Building regulations have to account for these possibilities they can't assume that you'll never have more than two 15 stone people at any one time standing on that area. They also have to assume that you are likely to be practicing start jumps !.

So in reality you can probably get away with not going to the trouble of being to spec. But it does then raise the question of what happens if someone does hurt themselves or when you come to sell the house what happens if an inspection turns up something that isn't right it would make it mighty difficult to sell.

Personally I'm planning on making our loft space useable for tidy easy access storage, so will be boarding out the loft and insulating rafters etc. But seeing as how I am likely to store heavy books up there I will build up the the 3x2's to 6x2's as I'm not confident that it will be strong enough otherwise, and enables me to put more insulation up there. I'm not going to the trouble of steal supports or anything complicated like that.

When you decide on the flooring material, just a suggestion but get 1 piece.
take it home & make sure that you can actually get that piece up into the loft.

It can be very embarrassing to find that you cannot get the load of sheets you have just had cut to size up there because its too long.