Loft Conversions and boarding

[redwineo]

I would love to convert my loft but don't really have the money to do it at the moment.
Is there a way of doing it bits at a a time?

I have started by insulating it and now want to board it. To do this I need to extend joists by 3". So what wood is best to use? I will need 2" x 3" x 4m lengths of wood but would like to know what would be best???
I can then lay my flooring straight across the loft.

Once this is done how expensive would it be to have the eaves (the two lengths of wood coming from roof to hold it up) removed?
Any help would be appreciated as have no clue and running out of space.

Cheers

 

[Deluks]

The first step would be to get a loft conversion company round for advice.

Unless you are very DIY savvy (by which I mean having quite a large clue on structural alterations plus the skills to carry out the work) then you will need the roof and floor structure upgraded by a professional, with calculations provided by a structural engineer to show to the building inspector when the time comes.

Without having this done, which will probably cost something between 4 to 6 grand, then there is little you can do by yourself bits at a time.

Whatever happens don't remove any part of the timber structure in the loft.

 

[ColJack]

the loft "floor" cannot just be put on top of the ceiling joists, they are designed to hold up the celing, not to support a floor..

often it's necesary to create a seperate "floating" floor with steel beams and 6x2's or bigger..
these floor joists should not contact the ceiling below as any movement of them will damage the existing ceiling.
the are often raised about 1/2 - 1 inch above the ceiling on packers resting on the load bearing walls etc..

 

[ajrobb]

the loft "floor" cannot just be put on top of the ceiling joists, they are designed to hold up the ceiling, not to support a floor..

I think that redwineo was hoping to stiffen/strengthen the ceiling joists with thick furring strips. I would like to know why, if you can make flitch beams by bolting wood to steel or engineered joists by spacing two beams with a pretty flimsy looking steel space frame, you can't gain strength by bolting wood to wood to increase the joist depth?

For instance, if I were to level a sloping/dished first floor with furring strips cut from a 50x100mm new timber and I attach the matching offcut to the bottom of the joists to level the ceiling below, would the treated joists (now 250mm deep) be much stiffer than the 150mm joists I started with?

 

[Deluks]

Yes, but not by much/enough. You will not get a fixing between the two that would be as strong as a single 250mm deep length of timber.

 

[ajrobb]

Yes, but not by much/enough. You will not get a fixing between the two that would be as strong as a single 250mm deep length of timber.

It is only a modest shear load at the centre of a rectangular beam. Much less than for the joints within an engineered beam. However, I suspect there could be creep at the wood-wood joint. So it might not be effective for static loads without some kind of glue or friction plate in the joint. But I suspect it would be a different story for dynamic loads. Furring out a 6" beam to 10" could give a dramatic improvement in stiffness and hence noise isolation.

 

[dhutch]

Yes, but not by much/enough. You will not get a fixing between the two that would be as strong as a single 250mm deep length of timber.

Depends how you stick it i guess.
- The size of modern screws/drivers you could plant a 4inch 10 in every 8inchs and i suspect it would do no where. Bung in some PU wood adheasive and it would be very stiff.

Im planning to board my loft but as it will be unheated need to extend mine from 4inchs to 10inchs in order to accomodate the insulation I intend to fit. Hence looking for threads on that.

Daniel

 

[jeds]

I would like to know why, if you can make flitch beams by bolting wood to steel or engineered joists by spacing two beams with a pretty flimsy looking steel space frame, you can't gain strength by bolting wood to wood to increase the joist depth?

To add to Deluks explanation. The problem with joining timber to timber in the vertical axis is that the force exerted by bending would tend to make the beam (joist) slip along the longitudinal axis. So what you would actually have is two beams of smaller section rather than one beam of matching dimensions. Of course you would gain some benefit but nowhere near as much as if you had a single timber joist of matching dimensions. And you would not really know exactly how much benefit which would make it difficult to calculate bending.

 

[dhutch]

To add to Deluks explanation. The problem with joining timber to timber in the vertical axis is that the force exerted by bending would tend to make the beam (joist) slip along the longitudinal axis. So what you would actually have is two beams of smaller section rather than one beam of matching dimensions. Of course you would gain some benefit but nowhere near as much as if you had a single timber joist of matching dimensions. And you would not really know exactly how much benefit which would make it difficult to calculate bending.

This certainly true.
- A 6*2 joist is about four times as stiff as a 3*2 joint, but two 3*2's is obvously only twice as stuff.
- Unless said, you can ge tthe interface between them sufficient to stop the sliding and make it actas one member, which as above, i would suggest you could with care.

 

[ajrobb]

This certainly true.
- A 6*2 joist is about four times as stiff as a 3*2 joint, but two 3*2's is obvously only twice as stuff.
- Unless said, you can ge tthe interface between them sufficient to stop the sliding and make it actas one member, which as above, i would suggest you could with care.

I guess the problem is trying to make a 'engineering' grade joint between an old joist and a new beam.

 

[dhutch]

I guess the problem is trying to make a 'engineering' grade joint between an old joist and a new beam.

True. Certainly if you where aiming to use a adhesive you would need to ensure the surface was atleast free from loose debri, and if it was a waney edge joint (not uncommon if you go back far enough) even a purely mechanical screwed joint would struggle.

 

[leew2]

Would fixing the extra piece with epoxy (to properly prepared surfaces) and big screws be almost as strong as a single piece?

I have an attic conversion (not done by myself) and the floor flexes underfoot which I don't like. I have thought about making the floor stiffer by bolting 8x2 joists to the side of the existing 2x4 joists and the putting the floor back.

 

[dhutch]

Would fixing the extra piece with epoxy (to properly prepared surfaces) and big screws be almost as strong as a single piece?

In a word, i would say, yes. But in that contect 'properly prepaired' could mean anything, and I would suggest that unless you run a plan or belt sander over it you time money on expoy would be wasted. Ive not done any calcs, but I suspect even just using a load of 4inch screws would be enough. 8*2 is fairly large on its own.

My uncal has an old cottage with 3*2 floor joists for the 1st floor and he had a lot of 'bounce' in the floor but as the floorboards form the ceiling (no pb) and all the ceilings already low, the options where limited. He opted to secure additoinal joists of 3*2, laid on there side, over the top of the existing floorboards and the refloor over the top in chipboard flooring. Screwed through with a lot of large screws. Other options would have resulted in a stiffer floor, but increase in stiffness was still huge, without reducing headroom by more than 3inchs all up, or damaging the aetheic of the underside of the floor. He also added a cut down pg topped in the voil to reduce sound transfer and add an amount of fire retardance.

Daniel