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How to raise a sunken room floor with timber?

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.

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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

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

EricL

Hello @nugley

If you get a larger window, then you won't need a brick layer, and you would technically save on one trade. Plus, you don't have to wait for the mortar to dry off which will allow you to install the window straight away. You don't have to search for matching bricks and reduces the labour involved in repositioning the existing frame.

Let me tag @Dave-1 and @Nailbag for their opinion on this.

If you need further assistance, please let us know.

Eric

Dave-1

Afternoon @nugley

Raising the window and the door would also mean shifting the Lintel above the door and window up, I havnt done one before by myself. Just something to keep in mind.

Dave

nugley

Thank you for the input @EricL. I'll check if a taller window can be fitted.

Thanks for your thoughts @Dave-1. Luckily I have space between the lintel and the tops of the window and door, so I might just need to get the builder to remove the cripple studs above the window and door and slide the window and door up to the lintel. Possibly avoiding the need to move the lintel.

nugley

As part of raising my sunken room floor, I'm interested in raising the room's aluminium sliding door and sliding window, which are external facing. The property is a late 1980s single-storey brick veneer home and the window and door are original to the home.

I believe there's a high chance that the door and window have nailing fins or flanges. From what I've researched online, the fins or flanges would need to be cut in order to remove the door and window and flangeless windows and doors would need to be installed in order to avoid removing the brick siding.

I'm just wondering, once the flanges are cut is it possible to reuse the window and door or would I need to replace them with new ones? Is it common to install flangeless doors and windows, and are there any drawbacks with flangeless?

JacobZ

Hi @nugley,

I've combined your new post with the one about raising your sunken floor as it provides some important context to the question.

The first thing I thought was that you would need to consider the lintels above the door and window, but I can see you have already considered this.

Your doors and windows don't look like they are flanged. Flanged windows would have an obvious border that would sit on the face of the brick on the outside of the widow and door opening. They look to just be a track and frame that is screwed to the brick around the opening.

If you can inspect the door and window frames, can you see any screws? Down into the ground and sideways into the brick?

Some up-close photos would certainly help our members work out the best way to remove them.

If they are simply screwed in place like I suspect, then they wouldn't be too hard to remove and reuse. If they are being raised, then you would need your builder to create space above the opening and then close in the bottom where it has been lifted.

Allow me to tag @Nailbag, @Dave-1 and @TedBear for their thoughts.

Jacob

Dave-1

Afternoon @nugley

Now this part of the question is something I havnt really delt with 🙂 I would be loooking for similar screws to the one @JacobZ has mentioned and reverse engineering it as I go. I generally try to make sure whatever I remove can be reused so get where you are coming from.

If the screws cant be removed due to age/fixing, I would drill their heads off if possible 🙂

Dave

nugley

Thank you for the replies @JacobZ and @Dave-1. I had a look at the window and door frames but there were only a few screws on each frame. However, I did manage to find an old photo of the wall when it was undergoing repairs back in the day. From the looks of the photo, the frames are attached to reveals and I noticed that Bunnings have a video on how to install an aluminium window. From what I understand, the architraves just need to be removed and the steps in the video would be followed in reverse to essentially remove the window and door. Do you reckon I'm on the right track?

I'd like to reuse the door but may look at getting a taller window attached to a reveal to save on the brickwork.

Also, I read that timber raised floors can be insulated to help muffle sounds when walking on them, but needs to be breathable to help with ventilation. From what I've seen there are several options such as rockwool, poly, eps and cork. I'm just wondering if you had any recommendations for insulating the timber raised floor?

Nailbag

Hi @nugley

Basically you would need to replicate all the supports and pull the plasterboard off as seen in the photo. But the issue is that the supporting beam above the door and window would need to be replaced with something less the height of your intended raised floor. This replacement beam would need to be specified by an engineer as its load bearing to the ceiling joists and rafters/trusses before starting the job.

Another idea you could consider is to leave the floor internally at the slider say 900mm deep by the sliders width. Then it's just an easy step up to the new raised floor. At around 170mm it deep enough not to be an accidentally trip hazard. If you considering how to allow air flow under the raised floor, install a coupler of ducted heating vents in the face of the step. All this would provide a considerable cost saving and a lot of work. And I think would functionally work fine.

Nailbag

nugley

Thanks for the input @Nailbag. Yes, it sounds like any adjustment made to this wall will need engineering evaluation. Hopefully the the gap between the tops of the window and door to the bottom of their lintels is at least 172mm or more, and just mostly involves removing the crippling studs. But if I go down this path, I'll ensure to engage an engineer.

However, I do like your step down option and will strongly consider it. I was thinking a step down that is 600mm deep and 2100mm wide would be nicer. But I would need to ensure it meets NCC standards. Thank you once again.

Nailbag

Your very welcome @nugley

When considering the depth (distance from door to raised floor) for the lower entry landing just has to be a distance that when you step down your not confronted with the sliding door and when entering your not faced with a step to soon or too far away.

Attached is an example of a similar raised floor idea for an underuse manacle I once made.

Nailbag

nugley

Thank you @Nailbag. I'll definitely need to consider a comfortable distance between the door and raised floor.

I like what you did to that place. Awesome work

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