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379 posts

Ultimate Geek
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Topic # 159832 14-Dec-2014 12:31
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Hi all,
I have embarked on the journey which will lead me to do the install of solid timber flooring onto existing particle board, in a DIY manner. I am confident with the use of necessary tools, I have most of them anyway, and there is tons of info out there. The installation method will be glued down and secret nailing.

The longest wall in the room is 7m long and in order to check the straightness of the wall, I have used two nails into the floor at each end of the wall and a string in between. The wall is perfect, but at the same time I have noticed that the floor is higher in the middle. While I have 20mm clearance at the ends (between the string and the floor), I can barely get 5mm in the middle. This tells me the floor is approx 15mm higher in the middle. I knew there is a bump there but I did not expect it to be so bad. I hoped sanding will get rid of that. The affected area is approx 3.5m x 2m, running along the central double joist of the house (right in the middle), perpendicular to the longest wall.

One way I can see this resolved would need serious work, as I believe the floor needs to be cut and removed, then use a planner on the joists and take 15mm out of their height. This sounds like something which I have a feel that it would NOT be recommended, especially as a DIY approach. The joist right under the bump is a double joist (running along the center of the house, which is a pole house construction, with two levels. I feel that reducing the joists height is a no-no.

The second solution I came up with, is more expensive and creates a lot of trouble with the floor level in the other areas, and is based on lifting the rest of the floor by 15mm, using maybe sheets of ply on the sides and then thinner ply (9-12mm) and then some leveling compound? Again, this does not sound like an easy DIY job, plus that you end up with huge level difference to other areas.

The third option I fell way more comfortable with, as it does not involve reducing the joists or adding (too much) extra weight to the floor. I am thinking to have the floor in that area not the way we all know the flooring is installed (sheets over joists), but to remove the particle board floor in that area and cut grooves on the back of the boards (with a router) which will allow it to go lower (the joists will get in the grooves). Then add extra nogs to support the floor and that's it. I will run new 4x2 "joists" on the sides of the original joists (between the new nogs) to support the "lowered" floor on the sides (the rule is always to have the edges supported, right?). The area under the floor is a closed garage with insulated walls, there is no wind or moisture in there, it is very dry. I can replace that area with ply as well if needed, but I do not really see the advantage. latest thought: maybe bracing in that area would be advisable?

I see the third idea to be perfectly doable as a DIY with the tools I have and does not affect the structural integrity. Also, the particle board will not have the thickness reduced by the excessive sanding process (which will diminish its capability to support the new flooring).

Any ideas or other solutions will be much appreciated.
The way I see it now, the third option does not have any downside.
Many thanks in advance.

And of course, I perfectly understand that whatever you tell me, it will not make you responsible for the outcome and it is my duty to get professional advice.

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5190 posts

Uber Geek
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  Reply # 1197216 14-Dec-2014 12:40
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I'd recheck the levels first. Doing it with a string line like that the line will droop in the middle and make it look worse than it really is. Use a laser level or if you feel like real diy then Google how to make a water level

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Uber Geek
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  Reply # 1197219 14-Dec-2014 12:46
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Sounds to me like the issue is more likely the piles/poles than anything else. Houses settle. The better solution may be to address the source of the problem, otherwise it may get worse with time.

I'd at least get an expert opinion.

Location: Dunedin


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  Reply # 1197249 14-Dec-2014 15:29
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+1 for both of the above answers. How old is the house?

379 posts

Ultimate Geek
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  Reply # 1197351 14-Dec-2014 18:39
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House is 30-35 years old, I agree it might be some settling occurring. There is no damage to walls / windows, it was absolutely no change in 5.5 years we have lived here.

I thought about the string bowing under its own weight, but I do not have a laser level. I will try to find one.
I will also try to get one of my mates (certified builder) to have a look at the situation and my idea of routing grooves into the old floor.

Thank you for the replies!

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Uber Geek
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  Reply # 1197494 14-Dec-2014 23:07
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If the builder's string line you used was tight, then it shouldn't droop much at all, a mm or so at most.
15mm hogging over 7m is really nothing to worry about, presuming it's even and not sharp bumps anywhere, then it's ~ < 1:200 gradient which should be unnoticeable. 
If there aren't noticeable localised humps (which might be able to be sanded) or hollows (which might be able to be filled with self-leveling compound) and there aren't any other issues (sticking doors/windoiws, cracks in plaster as you state), then you may still want to get a builder to look at it, but unless he identifies some specific issue, I suggest you do nothing at all. "Natural" settling tends to happen after constriction then slows down over the years.  If it's a subsidence issue etc (not likely from your description) then it's probably out of the field of expertise for a builder anyway, some engineering /geotech investigation may be needed, but by all means get the builder to check floor levels in general if you want peace of mind and and assurance.  
The new boards will flex enough to cope with the 15mm/3.5m curve.  Check the supplier's spec for tolerance for any small areas which may require filling or sanding. If the timber boards you're using are 19-21mm, then you don't actually need the particle board for support, so it can be sanded back locally until there's not much left.
My neighbour has been dealing with this issue with EQ damage to pole house, but humps in the floor were 30-40mm.  In that case some sub-floor work was done, temporary propping and notching some bearers and/or re-fixing one or two pole/bearer connections (bolted IIRC) - access was easy in most cases from underneath, but part of a sheet was cut out near one hump, work done, and a new bit of particle board put in. The floor was still not perfectly level after this.
He's used beech laminate boards, glued with hidden fixings.  Looks terrific.

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