Floor for bathroom

[shanesmith80]

Shown is what we have decided on for the layout for the bathroom reno.

It will be completely from scratch. Currently a suspended slab which will have questionable integrity after ripping up tiles, bath, etc. Plus this slab is higher than rest of house floor and want it either level or with a small step.

So first question. There are no bearers/joists under the bathroom. Double brick house with rendered brick internal walls. Room is 2600 x 1830. Joists run long way for rest of house. Will I need to put both bearers and joists in on peers or will a couple of joists attached with joist hangers and likely a small peer next to the wall be suffice for this short span. I would add hangers to the bearers as well.

Then for the floor. Would like to have the shower slightly lower than main room. Can I either notch an area down about 10mm on the joist for the shower floor area or add a 10mm packer strip to the main area to raise it up. Will likely go with sycon for the floor. Should I put some angle in where the 2 will join? I don't really see the point in this except to seal the ender of the flooring sheet, but this will be all painted and sealed with waterproofing.

Screen Shot 2018-12-22 at 18.33.53.jpg

Any advice greatly appreciated.
cheers
Shane

[Beardy]

1800c/c spacing for bearers is the traditional standard although that can increase depending on joist size
Keep in mind that you will need to incorporate termite protection with your subfloor timbers as well. Currently there is likely to be a 110mm skin of brickwork around the perimeter to support the slab but that will be too high for bearers and joists. I wouldn’t be in a hurry to discard the existing slab if it is reusable or even look to pour another one might be less work and expense.
Your shower floor needs to finish 10mm lower than the main floor but you normally still put the structural floor in at one level and set the various heights with your tile bed.
Dont forget you will need to waterproof before tiling as well

[ian]

Shane,
If you plan on ripping out the existing slab, doing so almost certainly counts as a "structural modification" requiring some form of formal approval -- either from an engineer or your local council, or both.
casting a new slab with a lower floor level should be straight forward -- you will probably only need to lower the edge supports for the existing slab. But, please, make sure you get the reinforcing detail right.
If you are planning on replacing the existing slab with something light weight -- like 18mm compressed fiber cement sheeting -- the hardest part might be removing the existing floor slab.

[shanesmith80]

Thanks for the feedback guys. Has been a lot of procrastination but moving ahead. Have worked out required screed heights to get the fall needed and that will give me my 10mm step into shower.

So the demo is going ahead and putting in the new floor.

Proposal below.
Ledger boards attached straight to internal brick walls, or with a spacer, jury seems to be out with that one. length 2600mm.

Joists attached with joist hangers. Spacing works out to be just under 400mm centers. More than happy to throw another in. The span across is1830 minus the thickness of ledger. All timber will likely be Hyspan LVL beams 200x45 or there abouts. Overkill?
Floor will be scyon or another compressed cement sheet.
According to my calculations, which are likely wildly wrong, this should be sufficient. If needed I am will ing to put in some piers and a bearer across the middle but that really seems overkill even for me.
Screen Shot 2019-01-23 at 20.48.53.jpg
Always open to other suggestions and feedback.
cheers
shane

[rwbuild]

What you are proposing is acceptable good practice, keep your sheet flooring at least 6mm clear around perimeter from brickwork and use stainless steel dyna bolts for ledger board and stainless screws for sheeting, make sure to drill a clearance hole in the sheets for the screws. DON'T use any silicon based sealants for joints , use the appropriated Sikaflex product for sealing joints.

[shanesmith80]

Thanks Ray. You are exactly who I was hoping would answer, much appreciated.

Can you recommend those Hyspan LVL beams or should I go hardwood? Is 200 x 45 overkill?

For the dyna bolts if using 45mm timber what would be an acceptable length into brick work? If using stainless for everything else I guess stainless screws/nails for the joist hangers too.


cheers
shane

[rwbuild]

Definitely use the LVL, no problems with shrinkage or bowing/cupping. Just be aware that you can nail at 90 deg to the vertical layers but you must screw when in same alignment as the veneers. Make sure you have plenty of cross flow ventilation under the floor.
Embedment into brickwork depends on the type of brick, if it is a dry press brick (solid, no manufactured extrusion holes in the body of the brick) 50mm minimum but I personally go 100mm, if it is an extruded brick (has holes in the body of the brick) 100mm, if it is a sandstock brick (made in colonial times) use chemset bolt anchors (Ramset).
Depending where the damp course is in the brickwork (if there is in fact any) I recommend 300mm wide plastic damp course taped to the face of the LVL against the brickwork to eliminate any chance of rising damp affecting the timber

[Beardy]

Agree with what Ray has advised, when you are bolting the plates to the brickwork you will be able to tell if they have engaged correctly or if you need to try a longer or perhaps different fixing type.
With the LVL be aware they sell a subfloor grade as well as standard, if you go on the suppliers website you will see spantables to check you have the correct size timber

[shanesmith80]

Thanks guys.
attached is the table i'm reading from and 200 x 45 is good for 4.5m, so my 1.8 should be well and truely overkill.

This is what I'm planning on using. https://buybuildingsupplies.com.au/t...-c-70_192.html

There is a damp course in the brick and will be line ball whether its over or under so will definitely go the plastic, thanks for that.

Not 100% on the bricks, but will try investigate. I will go 100mm anyway to be sure. House was built probably 1950's maybe 60's. Is double brick outside with solid brick walls right down to ground level with what I believe footings under each wall. Only access under house to each room is where a little door in the brick is cut out.

Air flow should be ok, have about 500mm clearance and it always seems quite dry under house when ever I'm under there.

Is stainless just a precaution or best practice? If all goes well with water proofing should never be and excess moisture down there.

Now speaking of overkill, would it pay to run maybe 3 bolts straight through wall to other side of ledger with some oversize washers to really secure along with the dyna bolts or am I just getting carried away. For the dyna bolt spacing I've read anything from 300 to 600 spacing. My thought was 2 rows offset with 600mm spacing in each row.
Screen Shot 2019-01-24 at 21.17.26.jpg

cheers
shane

[ian]

Thanks guys.
attached is the table i'm reading from and 200 x 45 is good for 4.5m, so my 1.8 should be well and truely overkill.

speaking as an engineer, that size (200 x 45) and span (1.8 m) is beyond bloody ridiculous -- but it's your money and you can waste it anyway you want.
Personally I'd be aiming at a size closer to one suitable for a 2 m span. Which might also lift the whole kit and caboodle above the existing damp course.

I have a feeling that stainless steel fittings may be a worse choice than galvanised ones. Stainless will happily rust if it's the wrong grade for the application.
A former neighbour who did some work for Sydney Trains once commented that a spec calling for stainless fittings for use inside a tunnel was a mistake, as galvanised fittings were more than good enough.

[rwbuild]

1 row bolts @600 centres is fine. Ian's comment size is valid, reference the chart and applicable size but allow for the additional weight of tiles and bath full of water. If the framing is above damp course, then gal bolts will be adequate.

[shanesmith80]

SO as thought the ledgers will be straddling the damp course.

As shown in the photo below of under the bathroom, the damp course is running on top of course shown with arrow. Problem is this row is running 90 degrees to the others, I'm assuming so they had something for the form for the suspended slab to sit on. This will make it hard to attach a ledger to the wall.

My question is can these be cut to finish flush with the rest off the wall? From what I can tell from looking at the other bricks forming the piers and from what you can see of these 90 degree bricks they are all solid bricks. Surely if they were the 3 hole ones then at least one of those holes would be visible.
Or am I going have to build in some piers?
IMG_1778.jpg

cheers
shane

[rwbuild]

They look like solid calsil bricks no holes but are not an overly dense brick and tend to fret under stress when dyna bolts are used. I would use bolts all the way through with a large square washer under the head/nut of the anchor bolt https://www.bunnings.com.au/macsim-1...-each_p0018441
Where is the internal wall above in relation to the corbelled (overhanging) brick coarse? If it is directly above the wall underneath then no problem removing the overhang BUT if the wall above is built off the concrete but directly over the overhang then that is a real issue. Can you check that first?

[Beardy]

Have you considered looking at replacing the slab again rather than the joist and CFC route? Price will be comparable and will be easier
Another option is to look at the various precast plank or Hebel floor options

[shanesmith80]

Where is the internal wall above in relation to the corbelled (overhanging) brick coarse? If it is directly above the wall underneath then no problem removing the overhang BUT if the wall above is built off the concrete but directly over the overhang then that is a real issue. Can you check that first?

By looking at the room with shared wall and from what it seems from where all the walls line up. The main wall is in line with lower coarse of bricks. On the other side of bathroom the overhang has a few gaps in it so I’m guessing it’s there for the slab form. Will go with the through bolts. If I don’t post an update tomorrow, the house has fallen over. 🤞 Cheers Shane