How to raise a sunken room floor with timber?

[nugley]

I have a late 1980s single storey brick veneer home built on a concrete slab. I have a sunken room floor measuring 5m x 4.44m x .172m and I'm interested in raising the floor to be flush with the neighbouring rooms. Change in elevation is 172mm.

Stud framing and drywalls sit on the sunken room floor, and one of the walls are along one of the external walls of the home. 

I'm interested in raising the floor with timber framing and placing insulation between the sleepers to muffle any hollow sounds when walking on top. I eventually plan to install hybrid floorboards on top. My questions are:

1. What type of pressure treated sleepers should I be using (e.g. H4) and dimensions?

2. Do I need a vapour barrier? If so, should I use a continuous vapour barrier and what type?

3. What type of insulation should I use (e.g. Rock wool)?

4. What type of subfloor should I add on top and thickness? I'm thinking structural ply.

Not sure if there are any other important questions I should ask or things to consider. But happy for commenters to expand on what I've asked as any input would be greatly appreciated, and a good learning experience for me.

 

[EricL]

Hello @nugley 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your flooring.

Generally speaking, if the concrete slab was built to code there would a vapour barrier installed inside of it. But if you wish to install one on the floor, standard builder's plastic should work just fine. I propose looking at using 140 x 45mm Outdoor Framing H3 Treated Pine - 4.8m as there is no direct soil contact, H3 treated timber should suffice. I suggest using 90x45 as noggins to support and stiffen the frame. I suggest using yellow tounge to cover the frame and using Floor Select 6mm 2.2m² Blackbutt Hybrid Waterproof Flooring on the surface.

Now adding all those materials up 140mm x 45mm + 19mm yellow tounge + 6mm hybrid flooring will give you 165mm which means that you are short by 7mm. You can use 2400 x 1200mm 7mm Plywood F8 Pine Structural CD Grade as a filler before placing the hybrid flooring on top. Before you start your project, your flooring frame needs to be safe and structurally sound. It must be able to carry people, appliances and other heavy items you might decide to put in that area. 

I therefore recommend engaging the services of a drafts person to draw up a framing plan for you. They will be able to calculate what timber size to use, how far apart they should be and what fixings will need to be used on the timber to keep it together. 

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric

[Dave-1]

Good Evening @nugley 

I like @EricL's recomendations about what sizing of the timbers and flooring to head towards plus using a drafts person. The main reason I am thinking of the draftsman is to make sure that the height from the floorboards to the ceiling is 2400mm, I am unsure what the ruling is but for some reason 2400mm height is in my head. If you raise the floor by the 172mm and you still have 2400mm head height there is no issue, if not then a draftsperson will know for sure and what allowances can be made.

Dave

[nugley]

Thank you for your input @Dave-1 and @EricL.This has helped me understand the materials needed and steps involved. It's a bit of a learning experience for me.

In terms of raising the floor by 172mm, the remaining head height will be 2400mm. Based on what you've said, it sounds like hiring a draftsperson is recommended even if I hire a builder or carpenter to do this job.

Is my understanding correct?

[Dave-1]

Good Morning @nugley 

With the height still 2400mm that makes things a lot easier, It comes down to what you want and how much you can afford. 

A drafts person can do the layout of the floor joists ect But a builder should be able to as well.

I would look for a registed builder, check their licence against the Department of fair trading for complaints (NSW has this) Check for past work by the builder, examples on social media and real people to talk to. Lastly I would not pay all the amount until its completed to your satisfaction. Materials and a bit yes at first, the final part at the end.

Dave

[EricL]

Hi @nugley 

Just to add to @Dave-1's excellent suggestions, make sure to ask them if they have experience in doing these types of projects. It would also not hurt to ask them for references or have a look at their social media postings as suggested by Dave. It's a good way to see the projects that they've worked on. 

Eric

[nugley]

Thank you @EricL and @Dave-1 @ for the helpful suggestions. I'll make sure to ask those questions and do those things when meeting with different builder

As part of raising a sunken room floor, I'm also looking to raise the existing sliding door and window in that room. Looking at the position of the cripple studs (a picture from past repair work) and the weatherboards outside, it appears this is possible without the need of any structural changes to the wall.

For the window, I'm just wondering if it's more cost effective to:

(a) replace the existing window with a new taller window. Avoiding the need to add new rows of bricks below the window or 

(b) raise the existing window and add new rows of bricks below the window.

Whilst this is something I will ask the builders, I'd be keen to hear your opinion on which one is more cost effective. Thank you.

 

[nugley]

 

[nugley]

 

[Nailbag]

Hi @nugley 

You actually don't require to use any special timber species. Standard MGP10 structural pine is fine being internal. The lower floor is greater than the min standard 2400mm. So bringing it up will not be an issue. Use 90mm x 35mm joists which may need to be packed to level less the flooring material. And you don't need a building permit or and professional drawings made up, at least in Vic. I did the exact same project 15 of years ago in this manor and was within build codes.

Nailbag