i want to lay a floor in my loft space. how do i strenghten my joists?

Answer 1

if the joists are exposed your best bet is to sister an in kind joist next to the existing joist to about double the load carring capacity.

or the next option is adding a load carrying beam below the joists 90 degrees to the existing near the center of their span.

adding something on top of the joists [either way] and covering over that would offer very limited benefits. and is really just a wasted effort.

you really don't give enough info. any intelligent and accurate answerer would have to have the type of construction, the joist span, size of joist, spacing of joist, type of joist material and their loading conditions at a minimum.

Answer 2

You don't give enough information for a definitive answer.
Roof type, ready made trusses, joist spans sizes,loading and purposes etc?
If it is something simple like using the roof space for light to med storage it you can improve the joist loading by fixing new joist alongside the existing joists, remembering to take the new joist right in to the eaves so that they sit on to the wall plate. That is the timber that sits on top of the last course of bricks.. Bear in mind that you have to get the new timber in to the loft space and in your average house the access is through the hatch on the landing. Not practical, Taking some tiles or slates off and coming in from the outside.is often the only way

It is not a job to be taken lightly without experienced help

If you are looking to improve the loading on larger, older beams without disrupting the whole building ask a firm called Rotafix, tel [phone] who specialise in is situ beam improvement on older, listed buildings.

Answer 3

if you want to properly strengthen the floor for use as a living space then follow the advice above.

If its just for storage you can either cross or counter batten the existing joist.

Cross batten - screw battens(unless drilled holes in the new battens) at 90 degrees on top of your existing ones. These should be at least 1" x 3" to make any difference and screw down through the 3" onto the joists - long screws needed. Dont use nail as your enthusiasm will knock plaster off the roof down stairs.

Counterbatten is the same as above, screwing on top of original joists or using coach bolting with wood load spreaders screw into joist side ways.

There are some very fancy joists, with a sheet of metal laminate between wood, but you are moving away from the DIY end again.

When you put a floor down, you need to leave room underneath for air to circulate (prevent damp - rot), counter battening helps air flow.

Answer 4

I would reccomend you contact a structural surveyor to come and check the condition of the beams and the type of timber used. This information would then proberly be best on to a civil engineer/ structural consultant that will then have to calculate the strengh of the current joists from dimensions span distance and timber type. A good structural engineer will be able to decide what reinforcement or replacement is required to meet your needs. If you decide to go forward an Engineer can often plan a scheme of temporary supports that are normally required to take the load of the roof during the replacement phase.

If you are lucky you may be able to get away with simply adding additional joists between the extisting ones reducing the Centre to Centre distance, this is the "easy" way because normally no temporary support will be needed whilst doing this.

The main thing I'd stress about this is, if you want it to be safe and meet current building standards the new design will have to be done by a Chartered Civil engineer.

Good Luck

Answer 5

Certainly the most secure way is to support the span from underneath. Just adding to the joists hardly adds support.

The issue is the span and the weight per square foot that will be applied to that span.

Steven Wolf

Answer 6

To strengthen the area you can add more joists. Without greater details on the situation I really can't give you anymore advice than that.

Answer 7

During the life of a house the joists will bend and warp a bit, to straighten them out will be very difficult and can cause more problems than it solves. If you buy interlocking loft flooring with the tongue and grove joints, there is no need to fasten them as much as you would with floor planking.

Answer 8

If its bowed plant a2"x2" that is 25x25 on the side that you need the overlap if its more than that put in an extra joist,
if its twisted you can iether lay battins on opposite runs, or cut spacers in to straighten, but this i would not advise it my pop the nails in the cieling below, and its a lot of work if that happens,

Answer 9

call in the professionals!