Thread: Loft storage area

I trust that you realise that if you noche the joists then the effective size of the joists is what is left. So say you noche your 90 x 35 joists by 20mm. Then the effective size of your joists will be 70 x 35.

May be I didn't understand your plan.
Although I can't see your setup, I question whether it will always be no walking by all people for the life of the building. Plus the standard 400 or 450mm spacing helps to keep the floor flat over time. A 800mm frame is considerably weaker than a 400mm frame. Then you are expecting to store things that are bound to be less than 800mm long.
In other words, I think you should have more joists.



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Minimum 180x45 H3 and DO NOT NOTCH them

Hi DaveVman,

I am looking to make a 15mm ply floor 3.6mX2.4m out of 3 full sheets of ply placed side by side. The sheets would be screwed to 4 3.6m long 90X35 standing on edge placed perpendicular to the 2.4m edge of the ply sheets. This would rest on two box section frames 50X25X3mm with 50mm edge vertical, attached to the shed frame. These frames are 3metres apart. There is only 800mm between this floor and the roof so definitely not designed for people or machinery. An oversized suspended shelf if you like. rwbuild has suggested that 90X35 would be too weak and I will rethink the notching probably opting for batten strap around the metal frame to tie the timbers to the metal frame. I can always add a couple of box section beams between the frames if sag becomes an issue. I can also keep any heavy items closer to the frame ends of the "shelf". The shed is designed and will only ever be a single storey setup. Thanks for the advice and hopefully I can get the box section frames made up this week.
Cheers,
Mac

I had a similar set up, very similar in height under the roof and it was great as long as you did not need to go up there often and get something from the back and then it was a proper PIA. I used posts from the workshop floor to support it and put up with the inconvenience. In the end I backed a trailer into the garage a few times and started throwing stuff into it and down to the tip it all went and I have not missed any of it that I am aware of. To make use of the space under the floor I put my benches and assorted things like grinders etc. It only had less than two metres head clearance under it but I have ducks disease so that didn't worry me at all.

Evening All,
So here is the result of the plan on the piece of paper.
IMG_0287.jpgIMG_0290.jpgIMG_0289.jpg
The end result is quite stiff and I was able to sit in the middle with little deflection. If I ever end up in the dog house I know where I can roll the swag out The bottom of the "joists" are attached to the support frame with angle brackets and the top is screwed to the ply. The ply is a neat fit between the angled uprights so they are locked and unable to roll over sideways. I will attach additional cross beams under the joists so I can store long skinny things under the floor. Someone didn't measure the distance between the battens and had to redo the angles I am looking forward to seeing the floor again.
Cheers,
Mac

Originally Posted by macandrita

I can always add a couple of box section beams between the frames if sag becomes an issue. I can also keep any heavy items closer to the frame ends of the "shelf". The shed is designed and will only ever be a single storey setup. Thanks for the advice and hopefully I can get the box section frames made up this week.
Cheers,
Mac

rwbuild might have some comment on this, but it's not just the floor sagging that I'd be worried about. You've created a single span floor, one end of which is supported only by the rafters/portal frame and is cantilevered. Your shed will have been engineered with roof loads only on the rafters, not the extra load of the suspended floor and whatever you put on it. The load on the rafters will be half the length between supports plus the cantilever. So 2.1m X 2.4m. And the way the load is supported on the portal frame means it wants to pull the rafters down which will want to push the walls out. I've seen this a lot in old timber frame sheds with non strutted King post trusses, people would stack timber on the tie beams and the added mass proved too much. Steel has better tensile performance, but it's something to be aware of.

Being in Mareeba, you probably get the odd cyclone so I'm guessing the portal frame is c180 or c200 lipped C channel and the portal elbows and apex joints are full wraparound and bolted through. That seems like it should support the load, but the wind loading has to be accounted for too. You're suspending mass from the roof, so that additional mass figures into the calcs. An engineers opinion wouldn't hurt given the location you're in.

RW & Richmond68 make very valid points to consider. This style of shed construction is only designed to support the structure and the wind region loadings for the site location. One point of failure is the ridge tie between the portal frame members at the inner end of your mezzanine shelf. Being 2400 wide also means that people will have to climb onto it to access items stored towards the middle of the mezzanine. All the best intentions go out the window over time so loads on the mezzanine will gradually increase.

JohnG has a shed in Tully that the ridge ties failed in Cyclone Yasi and now has a brilliant water collection system as the whole roof has inverted - and it had no other loads on the structure. You may also find your insurer will refuse to payout on a claim due to non-engineered modifications / additions to the structure. Another issue many victims of TC's Larry & Yasi etc have had to deal with.

It would be fair to assume the original shed design has not factored in extra loading to roof members. This being the case any load placed on the unsupported rafters would be over load. Your design has loaded the existing rafters at mid span, where they are at their weakest. Not good. May I suggest running a second rafter adjoining the back of the existing rafter, to which the support frame is attached. The existing roof structure has no collar ties. The addition of same to the stiffening rafters would increase load capacity. In fact, collar ties could have replaced your support frame.
The performance of your existing structure is extremely limited in load bearing ability. Be vewy vewy careful.

You have voided your insurance policy with what you have done. You better hope it doesn't go pancake shape with you under it either.
To maintain structural design integrity you will need to have a reconfigure the affected portal into a truss arrangement. What you have done negates all the design criteria for the structure. Contact the shed suppliers engineer for an approved design modification asap. I don't have the expertise to design/certify in steel even though I know what will be required, talk to the engineer.
The previous comments re storms and wind /rain loading a very valid.

Gentlemen,

Thank you for all your comments and advice. Let me first say that I have some engineering and agricultural background and as such have a reasonable grasp on what you are referring to. I have also built my fair share of implements so have a good understanding of steel properties. I have also experienced enough cyclones to last a life time including the big ones. Most damage I've seen occurs when the structure looses it's roof after a door or window blows in and inside pressure combines with low pressure on the lee side.
However I am also a good listener so have taken on board all that has been said. The steel frame is securely bolted to the portal so would be helping to brace the ridge joint. With any construction there are always safety factors built into the design so it is highly unlikely to collapse as soon as the design load is reached. While I am loathe to install a post in the middle of my work space, but I feel this may be the easiest way to support the floor frame thus removing the down load on the portal. I could also install a post under the end frame which would not be intrusive into the workspace. End wall already has a centre post so may not be essential. Centre support post just needs to be designed to allow boat mast to pass between top of upright and bottom of frame, grid iron goalpost style only with straight upright not curved.
Cheers
Mac

Do yourself a BIG favor, at the very least install a tie rod (16mm dia minimum or 25shs) across the portal frame effectively turning it into a simple fink truss (although, not a true fink truss) at least the portal will not spread and the tearing/shearing stresses on the bolts /knee and apex joints are substantially minimized.

Originally Posted by rwbuild

Do yourself a BIG favor, at the very least install a tie rod (16mm dia minimum or 25shs) across the portal frame effectively turning it into a simple fink truss (although, not a true fink truss) at least the portal will not spread and the tearing/shearing stresses on the bolts /knee and apex joints are substantially minimized.

In theory this would be a good idea, but unfortunately, in a C section built shed, there is little to anchor said tie rod too. Hence my suggestion for C section collar ties across the rafters at a convenient height.

Originally Posted by rustynail

In theory this would be a good idea, but unfortunately, in a C section built shed, there is little to anchor said tie rod too. Hence my suggestion for C section collar ties across the rafters at a convenient height.

If its fitted on the web side of the C section it is in the same stress plane as the web which would be the same as your suggestion of a C section collar tie.
Being in tension, it will always pull true to the alignment of the web on the columns and the rafters.

Hi guys,

Googled both Fink truss and collar ties and understand the directions you are coming from. I am inclined to turn the steel work into a proper Fink truss as it would only take 1 additional length of box to tie to the posts and the ridge. I am handy enough with welding gear to either do it in situ or set up to bolt on to the web side of the beams. Thanks for the advice.
Cheers,
Mac