help with new loft project

[andya]

hi all.do you think the head height is a bit low,am thinking of getting a dormer put on the back of the loft but dont want the hassle of getting a staircase.anyone know the best plan of action,would like a retracting loft ladder but if i get the dormer i assume you have to get a staircase.

[gizlaroc]

Looks about the same sort of head height as mine, and no problems at all for me.
We added a dormer to create just a landing so we could have a proper staircase going up, although in hindsight I wish we had carried the dormer the full width of the house at the back as it would have crested a room twice the size.
We were going to go for a paddle staircase but we wanted to get building regs, and they would noyt allow it, and I am glad that we went the whole hog.
We had to sell recently as I have jsut bought out my company and there is a 13 room apartment above the business, which I could not afford not to live in, having the proper staircase added over £40,000 to the sale price, compared with having a paddle stair, so the intial outlay of £3000 extra to do it (including dormer) now seems a no brainer.

Good luck

[seafoodmix]

if you do a "proper job" with the staircase and dormer etc and meet all the building regulations regarding fire doors, ceiling heights, heat loss etc you will be able to sell the house as having an additional bedroom, benefiting from the additional profit on the sale.

if all you do is board the loft and keep the loft ladder it will make a home cinema room for you but on sale of the property it is just a loft and will add no value at all.

you will however still need to check the strength of the existing joists and rafters to support the boarding and increased floor load etc.

[gizlaroc]

Yeah definitely check the strength of your joists, if they are only 4" you will find that you will be re platering the ceiling underneath every 6 months or so.

We had to put 8" joists in for bulding regs.

[Gary Lightfoot]

My house is a 30s build, and uses 6x2s for the floors, and 4x2s for the loft floor, as it only needs to support the bedroom ceilings. You can double the strength by screwing another 4x2 to each joist to make it the equivalent of 4x4. That's provided you decide not to go the whole hog for building regs etc.

Another way is to lay 4x2s across the existing beams and screw the new wood into each existing beam it crosses - it spreads the load more. You'll have 8ins of cavity for loft insualation and that helps a little towards fireproofing, though make sure the second layer travels across the top of the existing beams at 90deg so that it's not going to fall through if the ceiling gives way. Using special netting is probably a better idea. It depends on how far you eant to go with it all, considering how much/little time you'll be up there.

My ceiling height is 7ft or a little more, and no problems. I made a small 2ft wide ceiling for lighting and to hang the pj on, and that was the height that seemed a good compromise to the boarded floor.

HTH

Gary.

[seafoodmix]

Originally Posted by Gary Lightfoot

My house is a 30s build, and uses 6x2s for the floors, and 4x2s for the loft floor, as it only needs to support the bedroom ceilings. You can double the strength by screwing another 4x2 to each joist to make it the equivalent of 4x4. That's provided you decide not to go the whole hog for building regs etc.

Another way is to lay 4x2s across the existing beams and screw the new wood into each existing beam it crosses - it spreads the load more.

HTH

Gary.

At your peril !!!

The above methods may have strengthened someone else’s floor, but do not necessarily strengthen your floor. The methods described are structural solutions but they are not generic solutions and cannot be relied upon for your loft or any other without an assessment by a Structural Engineer.

Two 4x2 may be the equivalent of a 4x4, but if your lower floors span the same distance and 6x2 are required for those then it is a good pointer that the loft would require the same.

It’s best to do it right rather than risk damage to your property and you will not achieve Building regulations approval without supporting calculations for such work.

[Gary Lightfoot]

No peril involved, just simple physics - two 4x2s will offer more strength than a single 6x2 of the same material. It's a tried and trusted method called 'sistering':

http://www.hammerzone.com/archives/f...st1/sister.htm

US lumber is considerably smaller than the dimensions given - 4x2 is more like 1.5 x 3.5 so bear this in mind when reading US literature.

You find that in most cases, 4x2s at 14" centers across a normal span between walls is more than adequate to support normal loads (how much weight is in the average loft?), but 'live loads' (moving people etc) needs more support, hence a 50% increase to 6x2s with centers remaining the same in occupied floors.

Gary.

[seafoodmix]

[Quote]No peril involved, just simple physics - two 4x2s will offer more strength than a single 6x2 of the same material. [Quote]
Sistering timbers as the yanks have termed it does improve strength but two 4x2 joists nailed to make a 4x4 will never be a match for a 6x2 at the same centres whether sistered or whatever, if you nailed them on top of each to get a 8x2 maybe. As the yank web page states when a joist is in bending the extreme fibres are those with the highest stresses, hence depth is where it’s at. The calculation to check this uses the section modulas Z for the joist.
For a 4x2 Z=83300 mm3
for a 4x4 Z=167000mm3
for a 6x2 its 188000 mm3
for a 8x2 Z=333000mm3
That’s physics and indisputable.
Generally, bending is the critical condition for medium span joists, deflection for long span and shear for heavily loaded short spans or notched timbers. To pass building regulations the loft floor will be checked/designed for domestic live loads of 1.5KN/mm2 just like the upper floors in the house.

With structural work to your property (the most expensive thing you own) it is best to do it right, what works in someone else’s house will not necessarily work in yours. A lot of people “get a builder in” get the loft converted and its great, then they try to sell and someone requests the certificate to cover the works and you find you need to do a load more work (money) to do it right and get approval.

[Gary Lightfoot]

If you're to convert the loft to within the regs and make it into a habitable room, I agree a whole lot more work/skill/knowledge is required, including a full staircase and fire precautions to name but two. If you want to add value to your property, then getting it done properly is without question the only way to go. I don't believe you'll get approval other than by using steels for the new floor in most cases anyway.

Thanks for the Z figures - I appreciate the difference depth and width - would you say attaching a 2x2 onto a 4x2 is of a better strength than two 4x2s sistered? A 6x2 from the above figures is approx 13% stronger than a 4x4, so I was wondering how critical that would be. How much safety margin is built into the figures when calculating beam size?

Also, do they take into account the thickness and type of flooring used when calculating for loading etc?

How much strength, if any, is added buy adding 4x2 beams 90deg across the existing beams, being screwed to each on they come into contact with? At the point of contact, the beam is 8x2, but of course it isn't using the existing walls as supports, just merely spreading the load (and adding weight). Would supporting the new beams at the party walls be a better option in that case and sistering at the joins?

With your knowledge, would you consider writing a small contribution for others here who wish to strengthen their loft floor? Stating the best methods etc would be very helpful for others who wish to make their lofts sturdier for storage etc.

Gary.

[franc]

Someone told me about a new and fancy library that was planned and built for a university. Soon after opening, it was observed that the building was sinking!. The designers and structural engineers hadn't calculated the correct loading the books would create. I am unsure if this is true or not but its a nice tale all the same.

regards FRANC

[seafoodmix]

The problem with adapting existing joists is joining the two, what screws do you use and at what centres and what location. Because the joists have all ready taken up the load and deflected the extra bit of timber may never come into play. The safety margin for timber accounts for variation in the timber strength, no two trees are identical.

The dead loading should account for the floor finish, the boards, the joists, the plasterboard and the skim.

A floor is all ready a load sharing system, the load is spread by the floorboards onto more than one joist at a time. Adding a new layer of joists at 90 degress will provide no benefit if not fixed to the walls at each end. You are just adding dead weight. Between the joists where they cross the depth is still 4”. Joists normally span the shortest (most economical distance), if you rotate the span you may find that the supporting wall is not up to the job due to window openings or just lack of foundation. If you put load onto a party wall that was previous unloaded you should inform your neighbour (solicitor) and check its capacity also, you don’t want to get sued for a crack.

Faced with an un-boarded loft with 4x2’s when the rest of the house has 6x2’s (same centres and spans) I would put a 6x2 next to each 4x2 but a little higher. The existing 4x2’s would then carry on supporting the ceiling and all that dust and the new 6x2 would support the floor alone.

[Gary Lightfoot]

Some great info there - most helpful.

We get a lot of people wanting to convert their lofts, so hopefully you'll become our resident expert and myth exploder!

Thanks for your input.

Gary.

[leon]

if you need a loft ladder then this one that we use from colt in france
try this site...
www.dlcloft.com
we use the roto its 600mm x 1200 and its very stable. also there is a dorma that is factory made and comes in a kit form so no need for haste and a good diy person can fit them.