Insulation, Boarding and Structural Integrity

[tb1]

I have a typical 'W' trussed roof space and am keen to board out the loft space for more convenient storage of relatively light stuff. In order to maintain a reasonable level of insulation I will have to raise the void depth by adding 3" timbers at right angles before putting on the Chipboard flooring. I am concerned that the trusses will not take the weight. The span is approx. 17.5' and they are at 2' centres. The trusses are about 3' x 1.5'. Am I worrying unnecessarily? Can anyone help?

 

[JohnD]

It is true that the trusses are designed to be strong enough to hold up the ceiling (!) but everyone walks on them occasionally. You will probably find you have a great heavy water tank standing on a few trusses already.

I used the same method you describe, it spreads your weight across a few of the trusses and improves rigidity, it's worked well for me and I am quite lardy.

 

[Mr Winston]

truss calcs and designs always specify where the water tank is designed to go so normally if additional strngthening is required it is provided or spread over a suitable no. of trusses

A short term load like someone walking/crawling over trusses is different to a longer term permenant load say storage.

The answer is - it depends on what the loading the original design allowed for. If you dont know then you are taking a risk.

If your storing a lightweight xmas tree then i wouldnt be unduly concerned - but if you storing boxes of books/magazines/files then i would be concerned.

Remember that the extra 3x2 cross battens and flooring must be considered as part of the load

 

[masona]

Have a read here which may help you what to do.

 

[tb1]

Thanks for the responses. I will certainly not be putting up boxes of books and magazines but will be putting up all the usual baby cots, toys, suitcases etc. I have looked at the previous thread from masona and the roof design is very similar. I do not have the room to stand the additional joists off the wall plate as this would block the air flow from the sofit vents that I have also had to fit. (Another long story...following the cavity wall insulation overflowing and blocking the air flow thus causing a condensation problem!)

I believe that typical figures are 50kg\m2 static loading including loft boards and ceilings against a typical design static load of 25kg/m2 for roof trusses. (Add to this a factor of safety of 1.6 in the design process, spreading the load across trusses and the fact that I will not be boarding right up to the edges) I reckon that I should be ok as long as I don't get carried away and spread the load around the edges of the loft space.

Or am I barking mad!

 

[KonradFischer]

you should consider that it can not stop IR radiation which causes about 99% of thermal losses through walls and roof.

On the figure you can see the temperature after 10 min red light radiation on the opposite of insulation boards. This experiment (Lichtenfelser Experiment) I did together with some collegues and it is widely published, broadcasted and discussed in Germany. The materials from above are fiberglass, polystyrene, foam glass, solid brick, wood fiber board, gypsum card board and solid pinewood. Result: Some centimeters of solid wood will be enough for good thermal insulation, the lightweighters and the hypothesis of U-values you can forget.

Moreover there are no real proofs - and even the industry can give none - of the energy saving by additional thermal insulation with lightweighters. In opposite we have proofs, that the heating costs will rise after 'insulation' and mold attack will follow.

More details you can find here:

Thermal insulation and mold attack

 

[JohnD]

we have proofs, that the heating costs will rise after 'insulation'

opinions differ!!

 

[KonradFischer]

But proofs? The difficulty is to compare the efficiency of additional thermal lightweight insulation with the situation before.

And here I can offer a hit, which makes the german insulation industry more than nervous since years: Watching the heating costs of three big apartment buildings in Hannover over many years, they insulate Nr. 6 for 1 Million Marks in 1988 and then? Research for a lawsuit by my friend Prof. Fehrenberg, Uni of applied science in Hildesheim. But look for yourself:

Will this convince you? No and never? Why not - where are the real proofs for the opposite? Our insulation industry can not offer one! Yours?

See more to this topic here:

Thermal insulation without any good effect, but causing mould attack, asthma and allergies