Building a wood mezzanine in a cottage - advice & structural calcs?

[Nomad]

Hi, there. For an ongoing project of mine I'm looking at putting a wood mezzanine in the main room (partly as it's a tiny house with no storage, also for the possibility of putting a mattress up there as it's a good level to look out of the velux window and views will be rather special).

Ideas & suggestions welcome, especially dimensions for the main support beams.

The room & planned floor :


An idea of what I'm hoping for:



Requirements:
Length approx 8M / 24ft (I'll measure and confirm)
Spacing for beams 130cm (there's a gap on one wall that the beams will fit into, I can't alter this)
Width for flooring - maybe 140cm so I can put a double mattress up there?
Weight? Optimistically a lightweight bed + 1 large / 2 medium people at one end, bulky storage ( maybe some heavy tools??) at the other.
Minimum would be 1 person up there moving light bulky thing into storage.
No vertical supports to floor level (space is tight on the ground and having vertical beams supporting this will be a problem)
Weight limit?

For the future :
railings / fence to stop people & things falling off ! (legal railings are stage 3 and not needed yet, fitting the framework is stage 1, fitting the flooring is stage 2)
steps (I'm thinking a lightweight stepladder I can move onto position when needed)
Head height above will be limited but fine for storage or sitting up on a low bed.

I can do the building work myself but don't know what size support beams I need (I'm expecting to put a lintel into the end walls and rest the beams on that)
Tell me your thoughts

 

[gaz1]

your answer is no single bed only as the roof at the edge is too low for you to access it for a double matress up there

2 single matress can be fitted though and you can also create storage as well

 

[gaz1]

whats behind that wall all the way along it ?

 

[addjunkie]

I did very similar in one of my barn conversions. The timber accross the room at 8 m with no support will need to be a big steel. Its from memory roughly 6 m wide. I have the calcs somewhere for the beam. Joist sizes were just picked from the span tables for house upstairs flooring. The ledger was chem fixed into the back wall on 12mm studding. Joists are sculptured into the beam, every other one bolted to prevent movement. Beam is on concrete pad stones in the walls. Floor is tongue and grove ply glued and screwed rather than wayrock, as specified by the engineer who did the calcs.

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[Erie Fred]

The forum is called "MIG-Welding" and your asking about using wood.....
Structural steel would be my answer.

 

[Agroshield]

The 8m span is your biggest challenge. You need something that will meet the deflection criteria for the applied live and dead loads (which you should take from standard tables, not just make up numbers based on dieting for a week before you climb the ladder and only sleeping naked under a summer weight duvet).

You also need something shallow enough to maintain headroom below - it is not clear if the 2.27m is the underside of the structure or the mezzanine floor level. That is something to consider early on - the maximum structural depth of the new floor so neither above or below is too cramped.

If you know what you are doing, you can subscribe to this website for a month (and upgrade the subsciption to cover steel beams if a timber solution is not possible): https://www.timberbeamcalculator.co.uk/en-gb/ That will give you an idea of required section size.

A possibility for the 8m span beam using timber is what is called flitch beam - a steel plate sandwiched between two timbers.

There are a couple of practical issues: finding a piece of timber that is 8m long and dragging an 8m long piece of something into place from your driveway. If neither of these are an option, a structural engineer would need to design any joints/connections in the item to be used.

 

[gaz1]

if you take a look at this pic whilst its an apex point

it means you can fit single beds all the way down either side



the mattress can be on the floor itself

but i still need floor measurements of the room and whats on the outside of that wall

but like above that beam is going to be x2 12x4s but if the front to that wall is shorter its better to split the beam length as long as that wall is a supporting wall but you would still need a pillar

me personally id split the room into 2 depending on the windows and still have storage above the rooms as that room looks big enough for 2 double beds in a split room config then build a passageway to the other room external on the otherside of the wall

 

[Agroshield]

It is getting into the weeds and will be expensive, but if you absolutely could not have a column under the mezzanine floor, a complicated structural solution is to do something at roof level and have one or more tension supports (could be stainless steel rods) holding the mezzanine beam.

In other words, the mezzanine hangs from above.

Whatever is needed structurally might fit within the existing rafter depth in your initial picture and could span the same direction as the rafters. That also minimises the structural depth of the mezzanine so up and down headroom is maximised.

 

[Morrisman]

Looks to me that by the time the 24’ long crossbeam is in there, high enough to walk under comfortably while downstairs, there will hardly be room to crawl over it into the space behind it.

 

[Nomad]

Thanks everyone, answers in no particular order :
The left wall and the left 2/3 of the back wall are "old farmhouse" build (at least a foot thick, concrete both sides, infill a mix of rubble, cement, clay..), the right wall and right 1/3 of the back wall are new brickwork.
Good point about sourcing 24ft lengths of timber - I need to look at options, getting it on-site and into the room will be do-able with a helper.
Metal is my least preferred option for this (apologies - I know it's a welding forum ! )
The roof is quite new and was over-spec'd to allow for solar panels etc in the future, I had already thought about suspending some of the mez weight from the roof. It's an option and there are 10 roof beams so plenty of loadsharing.
A flitch beam (timbers & steel plate sandwich) is something i hadn't thought about, good idea.
I have furniture on the left wall that is 227cm high. Ideally the base of the new floor (ie top of the new beams) will be a fraction higher than this, this leaves head height of almost a meter above the front of the new mez, about 1.8m at the back. It's not ideal but at present it's wasted space in a house that has almost no floor space. Beams would be lower than this but it's an area where you don't walk around so some loss of head height is ok.

Keep the ideas coming, it's all appreciated

 

[addjunkie]

You can get various types of engineered joists, some with board in the middle others with like spring steel, posi joists.

Well worth investigating, but again not sure it will do the width.

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The timbers in my barn floor are 8”x2” off the top of my head the beam is 203x133 something like that. The bolt fixings are 6mm steel welded both sides. And 10mm bolts.

 

[gaz1]

you havent answered what ive asked

now i understand its a solid filled walls so fitting in a doorway will be fun to do

i also dont know where the windows are either but since ive split a french window into 2 to make one room into 2 is possible

now you have the width but still not provided full room size you only thinking of storage whilst im thinking of other things

one room ( 8m ) into 2 ( 4m ) big enough for 2 double beds to be fitted whilst that wall becomes a supporting wall for the beams i also have to warn about a wall plate soiled filled walls are different when fitting wall plates for beams to fasten too ( you will have to do research on soiled filled for fitting a wall plate to them every house is different as they are a compresive load bearing wall )

i also dont know whats on the otherside of that wall either cannot advise to create access of steps to the new storage area

also cannot advise if a hallway can easily be built either for access to the second bedroom you also dont state if its the rear of the property as windows can be fitted in the rear of the property font fitting is ackward as your changing the view of the property ( i get to use the change of view if next door gets consent to have the garage as the council has changed the front view of the property by allowing a garage to stay up that means i can fit another window in the front of the property )

 

[Nomad]

I thought I'd given all the info - looking again I missed some important things... thanks for the ideas everyone, special thanks to @gaz1

It's a tiny house/studio (open plan lounge / kitchen / bed + separate bathroom).
Windows: Front wall has 1 medium sized window (<1M wide, 1m high), roof has a medium velux (1.1m wide x 1m tall).
The original house had a partition wall and the rooms were tiny, splitting the room could work in other houses is but it's not an option in this house.
Main room size approx 8m wide, 4.5m deep, ceiling rises from a low of 2.2m at the front to just under 4m at the back wall.

Good idea about a dividing wall becoming a supporting wall for the mezzannine, sadly it's not an option in this house.
The filled solid wall is an unknown quantity, the surface layer was removed a couple of years ago, a heavy steel mesh fitted to reinforce / stabilize it, then new (concrete?) top layer fitted.Good point about any wall plates.
Access has to be from inside this room, as it's for occasional use (and any steps/stairs will have to be in the main living space) I'm expecting either a removable or hinged ladder (a hinged loft ladder would be a simple solution).

Adding more windows to the property is not an option. The back and side walls all have taller buildings adjoined. The front wall has no space (it's already fully used with door + window + kitchen units).

I'm thinking mainly storage (the house has none!) + maybe a day bed looking out of the velux. More beds won't add anything as the house is too small for 3 adults.

Keep the ideas coming, it's all appreciated

 

[gaz1]

8m x 4m can still be split and also window fitted with a velux windows

as goes for the split you can still do it as one room will be smaller as has to have a walkway through 1 bedroom for access

now kingsize beds are 5ft wide x 6ft to give you an idea of size and 4m is 12ft so plenty of room for a split of the room

can the wall be used as a split yes even with a door within it as the beams will sit upon the supporting support

access to the above floor should still be able to done if you support the roof and lower the wall only a door way access is needed

these pics was taken of a smaller double bed bedroom the frame was being fitted where that doorway was but i noticed it would be too small i got the owners of the building to move the wall right up to the staircase which allowed for a bigger bedroom for storage cupboards so was around 4m length but width is smaller than 4m

the doorway was blocked off after that

 

[addjunkie]

As its a small house, the stair shown by Gaz though compact wouldnt be anywhere near building regs compliant due to not enough head height at the top step. Also the base takes up a lot of floor space. A compact stair case incorporting a pillar could kill two birds withone stone. Pillar makes time joist doable, and stairs dont over burden the space. Perhaps even a cupboard behind the stairs.

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[sako243]

As its a small house, the stair shown by Gaz though compact wouldnt be anywhere near building regs compliant due to not enough head height at the top step.

Not that it's relevant but I think the property @Nomad is talking about isn't in the UK.

 

[gaz1]

the pics shown are to show a room of that size not the staircase

but that room can fit a double bed with bedside cabinets as well as storage at the back of the staircase for wardrobes the door that was fitted was to the left of the staircase

its about 4m length x 8-9ft wide ( 3m ) room size

if they want both rooms then access would have to be on the otherside of the wall or you could use a loft ladder with a hatch if only used like a loft area storage area

this one is the same but built above a kitchen

 

[carbonarc]

It has already been mentioned that steelwork would be a safe and effective solution to support this proposed suspended flooring.
Below is an assessment of circumstances if timber is used. It is based timber normally available in UK with an "E Value" [elastic modulus] of 8300 N/mm* and a density of 557 Kg/m*.
Using a nominal section of 200mm x 100mm and a beam length of 8.6m.
The beam will weigh around 90 Kg. When installed it will have a central deflection of somewhere near 11 mm. After installation of flooring with 18 mm sheeting and 150 x 50 cross beams the central deflection will increase close to 26 mm. When a floor loading of 1.5 Kn/m* is applied the central deflection increases to 134 mm and the maximum bending stress in the beam is around 17 N/mm*.
What are views on steel sections being used considering the 8 m free span?

 

[Nomad]

Many thanks everyone (especially the detailed infor from @carbonarc & @gaz1 ), lots for me to think about.

This thread has made me realise it's a lot more work than I was hoping for, I need to go away and think about my options.

This is wasted space at present and I'd like to make use of it.
Storage for light bulky items ( a wall shelf or suspended from the ceiling) would make a big difference in the house but I was hoping for more. It's not as easy as I'd hoped


Edits for background : as somebody mentioned above, the house is in Europe not UK so rules are a lot more relaxed - I'm happy using UK building regs as a template but internal works here don't need formal sign-off.

Edit2 : If it was in the UK I'd officially call this "Storage use only" but if it can be made so I can put a small mattress up there to enjoy the views it would be a big bonus. It has to be safe but doesn't need to be up to formal "bedroom with proper access" spec. Hope that makes sense

 

[gaz1]

remember you can do half of it if you want its the wall thats the most important part

or buy proper mezzanine 4.5m x 4m

for those that have mentioned fit woods from the soiled filled wall and fasten to the rafter beams

the issue lies with the soiled filled wall and the beam wall plate its not a concrete wall where you can just drill it and bolt it

the soiled filled walls are compression based do your due diligence if you intend to drill a wall beam

if your going to fit in a beam into that type of wall use blue slate and drill across a joint and slot that blue slate in as that will hold the soil filled wall stuff within and stop it dropping down