Loft boarding advice please

[Stotty1]

We have recently moved into our new house (built around the 1970’s) and we want to board our loft for extra storage.

I have been up and moved a section of the 200mm thick insulation out the way so I could see what I had to work with. It seems there are are 3 main beams (50mm x 100mm) running the length of the house between the 2 gable walls, spaced about 1.3m apart.
Then there are smaller beams (35mm x 70mm) running the opposite way under neath the 3 main beams, these are spaced about 460mm apart.
The ceiling boards then attach onto the bottom of the smaller beams.

My plan was to put 175mm stilts on the 35mm wide beams, relay the insulation and but the boards on top.
My question is though would the beams be strong enough to hold the weight and not cause the ceiling to bow?
Also would it be a problem that the stilts are only 175mm and the insulation is 200mm? I don’t want it to sweat as it’s been compressed slightly.

Thanks in advance for any advice

 

[Stotty1]

Here is a picture of the section I want to board first, in time I want to carry on and board the rest of the loft.

 

[JohnD]

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[Stotty1]

Is anyone able to offer any advice?
It would be greatly appreciated

 

[blup]

What is the span of the main joists i.e. end to end?

Blup

 

[Stotty1]

Thank you for the reply.

I do apologise if any of my details sound stupid I’m relatively new to this type of stuff.

I can only currently access about a third of the loft currently as the water tank is preventing access to the rest, but by the looks of it the 3 main joists (50 x 100mm) seem to join between the 2 gable walls which would be 10.4m.

The smaller beams (35 x 70mm) that run under the main joists go the width of the house 5.6m.
These look as though they bolt into the main angled beams that form the apex of the roof.

I will add some pictures to try and help with my terrible description

 

[blup]

I would be surprised if 4 x 2" joists had an unsupported span of 10.4 metres: are there any load bearing walls that support these joists along their length, and, if so, at what points?

Blup

 

[Stotty1]

Been round checking the walls and all the internal walls upstairs are stud walls, the only solid feature internally is the chimney, which is around 3.5m in from the front gable wall.
So I’m wondering if that is why there are these extra beams spaced down the loft, that prevent it from being one big open space.

Thanks

 

[blup]

A roof could be a simple wooden triangle but to make the beams a more manageable size various struts, purlins and other timbers are used to strengthen and stiffen the structure, so allowing smaller beams to be used - that is why there are so many pieces of interconnected timber in the loft.

In your case that means the loft is possibly only designed to take the weight of the ceiling and not much more, perhaps the occasional human visitor

I am no expert but I would query the wisdom of adding anything more than the additional insulation and some fairly nominal storage. I don't see how plastic stilts would be stable with 1.3 metre gaps between the main joists

If you wanted to go ahead a structural engineer would need to do loading calculations for you, or alternatively an experienced builder could look over it for you.

Blup

 

[ray.birch]

Are your main beams definitely 4x2? They look as though they might be 6x2 from some of the pictures, but hard to say for sure. Just wanted to check!!

 

[blup]

Also take into account that with a 1.3 metre spacing between the main joists, chipboard flooring would fail as it needs a minimum of around 14/16" inch centres to properly support the weight of a person.

With 6 x 2" joists that might be achieved by suitably fixing beams at 90 degrees.

Blup

 

[Stotty1]

Thank you for your help, been back up and double checked they are defenetly 4x2.

My original plan was I was going to put the 175mm stilts on the smaller (35x70mm) beams to achieve the correct spacing. So the chipboard would never have touched the joists as they would be 75mm above them. I was just worried the beams wouldn’t be able to hold the weight.

My thinking is now could I go with my original plan and put some 75mm Battons ontop of joists at 90 degrees bridging the 1.3m gap. That way the stilts will support the chipboard adequately but the extra battons will help spread the load onto the joists. Or would that still cause problems?
I hope that makes sense

I now understand no matter what I do I would have to keep the weight to a minimum due to the length of the joists with no central support

 

[blup]

No, not as you describe the spans and joist sizes.

I suspect there are supporting walls as 4 x 2 normally has a specified (albeit conservative) span of around 2 metres according to the tables, not 10.4 metres.

You can often tell if a wall in the house is structural i.e. in this case load bearing of a roof joist, if it rises from ground floor to first floor and is solid brick or block, double skin.

Blup