Does adding wood to the top of joists reinforce them?

[wizard]

I'm intending to board out my loft for light storage, and have just reached the stage where I'm going to insulate the loft floor. My current joists are 38x63mm, so there's no space for rockwool insulation at the moment.

I'm trying to decide whether to go for something thinner like kingspan, or whether to raise the joist level by adding more wood to the top. What I wondered is, would adding more wood to the top of the joists (say another 38x63mm timber) add to the rigidity and strength of the joists, or would the extra weight make them weaker?

If I were to add to the top of the joists, the extra timbers would have to be in a couple of sections as the span is too great for a single piece, but they would be supported by the existing binders and hangers from the purlins - does anyone have any idea what effect this would have on the strength?

Any advice/suggestions that anyone could offer would be much appreciated - there certainly seems to be plenty of expertise in here.

 

[chappers]

yep would help to a certain degree if you use enough screws but the resulting timber would not be as strong as a single piece of the same dimensions

 

[wizard]

Thanks for the advice, very helpful

 

[masona]

You maybe better off putting 4"x2" timber along the side of the ex-joists resting on each end of wallplate and screw to the side.

 

[wizard]

That was my other thought, but there are three spans of about 5 feet from the centre supporting wall to the outside walls. If I put in extra timbers by the side of the existing joists, would they be OK supported by the existing hangers from the purlins (about 8x3) at five foot intervals (I don't think I can get 15 foot timbers in through the hatch)?

I don't think it's essential to beef up the timbers I've got at the moment, as I'm only really planning on storing empty cardboard boxes ( packaging for TV and so on) and stuff in there, but I just wondered if I could combine the insulation method with strength increase. I guess it'll probably come down to cost in the end.

 

[Thermo]

id be inclined to run them side by side with the existing and bolt them through as well.

Thermo