Attic/Loft Joists

[RobbieP14383]

Hi I have just bought a house with that seems to be a very weak attic. The joists in the attic are on 80mm deep and I have been up there a few times recently to put a light and rewire the upstairs lighting. Since I have done this there are holes appearing in the ceiling below where it has been nailed up and you can see the plaster has or is coming away and revealing said nails.

I have a semi detached house with a pitched roof to 3 sides. The majority of the timbers run from front to back and are as mentioned 80mm deep only. Laying directly on top of these timbers are 2 175mm deep joists that are 4 metres apart and the same distance away from either end of the house which is about 1.5 metres.
The width of the house is 5 metres and length from front to back is 7.35 metres.
I would like to strengthen the attic considerably to allow for storage and obviously the weight of a few people.

What is the best way to accomplish this?

The loft hatch is about 300mm square. I was thinking to buy more 175mm joists and lay them on top in a similar fashion to the existing 2, however getting them up there would be a challenge, I would need shorted lengths and then join them somewhere in the centre section with an overlap. In my opinion this would comprise the strength at the join?

Your advice is appreciated.

Many thanks

 

[loply]

I presume the attic isn't boarded? ie floor boards of some kind?

If not then simply boarding it may be the first point of call, as it means that your weight is distributed over a larger number of these weak joists when you walk up there.

Use tongue and groove chipboards and lay them lengthwise across the joists so as to spread the load as widely as possible.

Putting extra joists on top of the old joists will just increase the load on them, unless you plan to always walk along these extra ones?

 

[RobbieP14383]

Hey, thanks for your reply.

There are currently no floor boards in the attic.
Part of my thinking was that I want to increase the depth of insulation in the attic also, combining the depth of the 80mm timber and 175mm timber being laid on top would give me a depth of 255mm of insulation. I would then be putting the tongue and groove flooring on top of the new 175mm joists just laid. I would lay the new joists about 250mm apart and then screw the floor boards down on top.

Thanks for your advice.

 

[loply]

So you're talking about building a new set of joists perpendicular to the old ones in order to increase the depth for more insulation, and distribute the loads when walking up there?

The only trouble is by the time you add all the new joists plus the boards you may be putting quite a bit of extra weight on the old joists, albeit distributed quite evenly.

Why not just go for a thinner insulation which is better U value? Saves on the weight, cost and hassle of your extra joists. Or better yet, insulate the roof instead of the ceiling, if you insulate just the ceiling there's a chance you'll get condensation on the inside of the roof which may be an issue if you're going to store things up there.

In my experience many lofts, even on new buildings, will start to pop plasterboard screws when you walk around in them without boarding. I don't think your joists need reinforcing with new joists, they just need boarding.

Alternatively, just eat less hobnobs. Or get the wife to put away / retrieve the Christmas tree when required