Question on Loft Boarding

[steveoelliott]

Hi all,

I have a question regarding my loft boarding, which a friend (who is very skilled in DIY / Carpentry) did for me. The centre of my loft is boarded (the middle of the W)

I have a W shape roof truss and his recommendation was to not simply raise the ceiling joists / bottom chords and then attach boards to these, but rather to create a suspended floor by screwing lengths of CLS to the web trusses with 2 screws at either end and then screwing 22mm thick chipboard to these. The CLS does also have 2 noggins which are screwed into the rear of the CLS with a single screw and then secured to the bottom chord with another screw, screwed diagonally.

In fairness my loft boarding does look very good, all is nice tight and level and it creaks less than the floor boards in downstairs lol (in fact hardly at all). It's very tight.

I just wonder how safe this is? My friend ensures me that due to the clamping force exerted by the CLS to the truss, the screws don't bear as much load as you think (and they are long wood screws) and also the strength is combined in the entire structure. He ensures me that it is more likely the roof collapse due to the weight you could put up there before the new boarding support structure would fail.

Untitled

• steveoelliott
• 4 Apr 2014
• 1

Thoughts???

 

[tony1851]

Roof trusses are designed to take; the dead load of the roof structure itself (tiles + battens + plaster board + truss self-weight etc) plus the snow load, plus a provision for light storage in the loft itself, at no more than 5 psf, sensibly distributed.

No matter how the additional framework is arranged, there is this limit to consider. There is a risk that building a supposedly rigid structure would enable you to support more than the truss is capable of.

These things are carefully engineered and ad-hoc fixings to them can invalidate the loading assumptions.

 

[freddiemercurystwin]

Roof trusses are designed to take; the dead load of the roof structure itself (tiles + battens + plaster board + truss self-weight etc) plus the snow load, plus a provision for light storage in the loft itself, at no more than 5 psf, sensibly distributed.

+ a couple of hairy arsed builders waking about on the bottom chords during construction.

 

[tony1851]

Roof trusses are designed to take; the dead load of the roof structure itself (tiles + battens + plaster board + truss self-weight etc) plus the snow load, plus a provision for light storage in the loft itself, at no more than 5 psf, sensibly distributed.

+ a couple of hairy a***d builders waking about on the bottom chords during construction.

Yes, but the fat hairy ***** builders only represent a temporary imposed load, and the timber code allows increased stresses for temp. loads.

 

[steveoelliott]

I understand that this type of construction would allow me to potentially put 1000's of kilos of weight on the boards but I am sensible about this.

Most of what is stored across the fairly large space is light(ish).

It is secondary storage and no more than an average person would have in their loft.

It was just for convenience and to make walking around up there easy.

My question is to whether it is safe. Obviously I am not asking for a guarantee as anything given is based on assumptions but in principle is what I mean.

 

[tony1851]

In practice, if you're sensible about the loading, it may well work. But no-one here - and certainly not the original truss manufacturers - will confirm 100% that it will be OK.

 

[steveoelliott]

I understand...

In my lifetime I have not seen a roof collapse due to overloading and I've seen folks with s**t loads in their lofts.

I do know and appreciate that newer houses are far weaker than the older ones though with far less support. The trusses / rafters in my loft are thinner than my parents for example.

 

[tony1851]

The trusses / rafters in my loft are thinner than my parents for example.

That's another reason you should be very careful when screwing into them; there is a risk of splitting the timber,particularly if done near a node.

 

[freddiemercurystwin]

tony and the other disbelievers would have fit if they’d seen some of the stuff I’ve stored in trussed lofts. And ……… I’m still alive and the house didn’t collapse!

 

[steveoelliott]

Yea... My question was more around the way in which the floor supporting structure was put in place.

My first question to my friend was, how can we just rely on screws to hold the suspended floor up. However, he explained the combined strength of the structure, clamping force and noggins were more than adequate to support anything sensible being stored up there.

His point to me was, in order for his structure to fail / collapse, it would require more weight / load than the loft could handle. i.e. the trusses would collapse before his structure did.