When to double up trimming and trimmer joists?

[RossJarvis]

I've been scouring the inter web and am very confuzzled now.

In regards to trimming a joist for a mezzanine floor in an outbuilding (workshop, no not a workshop, it's sort of a large shed Mr Planning Officer). A hatchway for an access stair (loft ladder actually!) into the mezzanine floor will cut through one joist. The length of joist is 4m, size 150x50, 400mm centres. Do the trimmers (headers) need to be doubled up and do the trimming joists need to be doubled up? The mezzanine is likely to be used frequently.

Thanks if anyone can come up with an answer. The "ahem" shed is liable for building control.

 

[Woodchips2]

Hi Ross
If you are creating a mezzanine floor for frequent use with joists spanning 4m then 150x50mm joists seem a bit small. The old rule of thumb for depth of floor joists was span divided by 2 plus 2 inches. 4 Metres is 13 ft so 200x50 or even 225x50 if you don't go to Slimmers World on a regular basis.

I would double up on trimmers and trimming joists but I am cautious by nature :lol:

Regards Keith

 

[RossJarvis]

Hi Ross
If you are creating a mezzanine floor for frequent use with joists spanning 4m then 150x50mm joists seem a bit small.

Regards Keith

Thanks Keith, I'm going by memory (and can usually just remember my own name) the joists may well be 8x4.

I haven't found anything definitive yet, but did see something that mentioned doubled trimmers and trimming on anything where the span between trimmers was 4' (1200mm) or above, but this didn't mention length of joists. I'm just thinking the trimmed joist, headers, ladder and box are now mainly additional dead weight so doubling everything seems the cautious route. This is a deviation from the engineers spec and they cost an arm and a leg to just answer the phone let alone look at any alterations :shock:

 

[Lester Burnham]

Not sure if this helps but I am converting a barn at the moment and putting in a new first floor. Span is 4.3 metres and joists 450 centres. I am trimming an area of about 2metres to allow for a staircase, and the area within the smaller trimmed floorspace will house a bathroom. My structural engineer requires my joists to be 225 x 75 and to simply double up the trimming joists. I have also doubled up the trimmer. I hope this helps as the cost of his calculations far exceeds the work to do this and I will be delighted for others to benefit from his sums!

regards.
LB.

 

[RossJarvis]

I hope this helps as the cost of his calculations far exceeds the work to do this and I will be delighted for others to benefit from his sums!

regards.
LB.

Thanks Lester