How to fix a breaking floor in a transportable building?

[Carroaust]

Hi, we have an approximately 15-year-old transportable building in which the subfloor unfortunately is starting to break. We can feel that it is quite "bouncy" in spots, and it has cracked in one spot already. We think it's made of some sort of plastic/composite material, and it seems to be made up of a top and bottom flat surface with vertical supports (the building is elevated so we could look from underneath and it seems the same structure as from the inside). The area is approximately 14m2 and is made up of one office room with an adjoining small bathroom (the door between these two rooms can't be closed at the moment due to the floor protruding slightly). 

We live in a rural area so it's not easy for us to get a builder to come and have a look at it, so we are hoping that we can get some assistance to hopefully do a DIY fix. From the bit of research we have done one option we are considering is laying a new subfloor over this floor. However, we are not sure what type of boards to look for in that case, as Bunnings seems to have a lot of options for sale. We are also wondering if placing laminate or hybrid floorboards would be sturdy enough. Or if we need to combine the two (new subfloor + floorboards on top). If anyone could offer some advice we would really appreciate it. 

Thanks a lot in advance.
/Glen

[MitchellMc]

Welcome to the Bunnings Workshop community Glen (@Carroaust). It's brilliant to have you join us, and many thanks for your question about repairing a subfloor.

Adding laminate or hybrid floorboard on top of a compromised floor will not resolve the issues present. So, it would be best to concentrate on repairing the floor first. Given this is some type of specialised construction, we'd need some additional details and images to help formulate solutions. Let me know if you need a hand uploading images.

Is there some type of frame that this floor sits on? Can you tell whether this is a structural issue with the frame or whether the flooring itself has deteriorated? Can you tell what is making some spots bouncy and others not? If a sub-frame is present, could you replace the existing floor with something like structural flooring? I think it's important that we sort out or replace the existing floor so you have a solid base to work with. From there, you'll be able to add whatever flooring you desire.

Please let me know if you have any questions.

Mitchell
 

[Carroaust]

Hi Mitchell,

Thank you very much for your reply, I really appreciate it.

The building is an Edilsider transportable building. I have attached a floorplan with dimensions. I took some photos underneath which show the C-section joists the floor sits on. The joists are spaced 600mm apart. From what I can tell, the floor sits directly on the joists. I tried to look at the floor where the cutout for the shower drain is, and it looks like the floor has a top and bottom flat surface with vertical supports, if that makes sense. Unfortunately, I couldn't get a photo since it was such a small gap I could only feel with my fingers. But it would be like a "H" on it's side 90 degrees I would say. It feels like some sort of plastic/composite material, not timber.

I think that it's the flooring itself that has deteriorated since I can't see an issue from underneath. The spacing of the joists seems quite wide, so I suspect that it puts greater pressure on the floor. We bought it used so we don't know its previous history, so we don't know why some parts of the floor are bouncy, but it's worse in the middle of the room where supposedly it has seen more traffic going to and from the bathroom.

Do you think it would be possible to put the yellow-tongue flooring you linked to on top of the existing bouncy floor? 

Thanks again for your assistance. Cheers, Glen

[MitchellMc]

Adding the yellow tongue to the existing flooring would likely work, Glen (@Carroaust). Just remember that you're going to raise your floor height by 19mm, so consider if this is will cause issues in other areas. 

I guess the other option would be to install additional timber joists or noggins underneath to help support the floor. If you could provide enough support to stop the bounce, then that opens up the option of installing Hybrid flooring. Hybrid flooring will provide some additional stiffness to the floor, but I think additional measures need to be taken in case this issue worsens and the floor continues to deteriorate.

Mitchell

[Carroaust]

Thank you very much, Mitchell. I think we'll go with adding yellow tongue, since I don't know if we'll be able to support the existing floor enough or if it will continue to deteriorate. Are the boards you linked to suitable to use even in the bathroom? Can we add hybrid flooring on top of those boards for appearance?

Thanks a lot for your help, much appreciated. Cheers, Glen

[MitchellMc]

What type of exposure to water will the structural flooring see Glen (@Carroaust)? The structural flooring is fairly resistant to water as it's designed to be left uncovered for a few months in building construction, but it will deteriorate eventually. If you use it in a wet area, I'd recommend you paint it with a waterproof membrane like the water-based bitumen paint (which has little to no smell even whilst curing) and then lay Hybrid flooring over the top. Hybrid flooring itself is water-proof, but that doesn't mean that water won't find its way down to the chipboard if the bathroom is regularly flooded with water. Is the shower an enclosed cubicle, or is it a wet area bathroom where the floor sees plenty of water?

Mitchell

[Carroaust]

Thanks for your recommendations, Mitchell. The floor of the bathroom wouldn't get flooded with water, but it does get a little bit wet when we exit the shower. It is a shower base with fairly high sides and we use a shower curtain. We use absorbent floor mats which we dry between uses, so the surface doesn't stay wet for long. However, we probably will apply the paint that you recommended just to be on the safe side. 

Another quick question, what do you recommend for fastening the boards to the existing floor? I know it's difficult since we don't know what the existing floor is made of, but since we probably won't be able to screw in to the joists, do you think just nailing or screwing it down to the existing floor will be sufficient?

Thank you. Cheers, Glen

[MitchellMc]

Provided it's well fitted, it will stay where you put it @Carroaust. I would suggest that screwing through the boards into the old floor would be sufficient to hold it in place. The flooring comes with tounges that lock the boards together into one large piece.

How well you can attach it to the old flooring comes down to how thick that top layer of the H is. I'd imagine simply fixing it down every 60cm with screws will suffice.

Mitchell

[Carroaust]

Thank you so much, Mitchell, for all your advice. We really appreciate it. We will visit Bunnings this week to get the supplies for this project.

[MitchellMc]

Keep us updated, Glen (@Carroaust), and please reach out again if you get stuck or have further questions.

Mitchell