Sagging floors in upstair bedrooms 1930s house

[Shesh222]

Hi there I bought our 1930 house two years ago in August. When purchasing we never really noticed the sagging bouncy floors in the 2 main bedrooms upstairs. It just felt like a normal old house. (The house was empty, no furniture). Pre purchase I had a structural engineer do a general structural survey. Mainly to check over the two old extensions and some cracks to the external render. No urgent serious issues were mentioned in his report, and he made no mention of any problems with the bedroom floors. He said there was some sign of old normal historical settlement movement but nothing recent or concerning.
Below the bedrooms there has been a wall removed between the two reception rooms downstairs to create one big living room. There has also been a chimney breast removed but the other still remains. Again the engineer just stated there are beams in place and nothing suggests theres anything structurally unsound with them. Ive been told by a neighbour the ceilings in the living room are all still lath and plaster and you can see some bulging through the ceiling wall paper the previous owners put up. Which im guessing would be cracks once the paper comes off. So i know the ceilings will need replacing. Or at least boarding over if thats possible . Cant wait for that epic dusty mess.
My issue is is that both the floors themselves of these bedrooms sag in the middle. Theres no sag to the living room floor. How do i measure it accurately to know how severe it is? Im struggling to understand how you work out the severity of it. As in so many inches sag over a certain span. So what? I measure the whole room size one end to the other and see what the dip is in the middle? In the two years weve lived here i havent noticed that it has got worse. But it is noticeable enough. The tilt on the furniture all appears the same as it was . Not any worse. How do we check the floor joists? Im so annoyed because i had my dad fit some lamimate for me as we had to take up the disgusting carpets and neither of us thought about checking under the floorboards at the time. So now it's more of a faff i guess. Hes a bit blah se and says its just a normal old house and wont fall down. I try and think that way but its still in the back of my head at times because my son is in one of said bedrooms. How big should the joists be ideally? What remedial work needs doing if any? Will it fall through or not. If i need to get someone to assess it who should do it? Im very reluctant to pay another engineer as quite frankly im cheesed off this one made no mention of it in the first place. Having looked at the report again it doesnt even appear he even looked in the bedrooms. Which leaves me with little trust in these surveyors. Is it even worth doing if its stable enough. I can live with it if its just normal deflection and therefore old house character.

 

[Deleted member 174758]

How do we check the floor joists? Im so annoyed because i had my dad fit some lamimate for me as we had to take up the disgusting carpets and neither of us thought about checking under the floorboards at the time.

The quickest way to see the bow is often to just plonk a 6ft level or other long straight edge (e.g. straight piece of planed timber - but it must be dead straight, such as s piece of Contiplas shelving would be, edge on) onto the floor. If the floor is relatively flat you may see a couple of millimetres of gap beneath the straight edge, but a badly bowed floor is really obvious

My issue is is that both the floors themselves of these bedrooms sag in the middle. Theres no sag to the living room floor. How do i measure it accurately to know how severe it is? Im struggling to understand how you work out the severity of it.

The best way to get an accurate picture is to completely empty the room of furnishings and carpets then fix a laser level to the wall in one corner at about 1 metre above floor level. You then make up a staff - basically a piece of straight 2 x 1in (44 x 22mm) planed softwood which is 8in (or a couple of hundred millimetres) longer than the laser is off the floor. Hold the staff vertically in the corner with the bottom on the floor and pivot it back and forth so you can see where the lowest point that the laser highlights is. When the laser line is at the lowest point the staff is vertical. Mark that point on the staff and draw a line across the staff using a try square or set square. This is your corner datum line. It will make measuring easier if you mark increments up and down the staff from your datum line every 3 or 5mm for 20 to 30mm. Now go around the room using the staff with the same "waggle technique" to check the distance above or below the datum line on the rod that the laser shows. Write this on the floor at that point (with Sharpie) as the dufference value with plus numbers for the laser showing above the staff's datum line (e.g. "+12") or minus for below (e.g. "-6"). When you have gone round the room checking every metre or so you will be able to tell if the floor slopes and how much the bow is. The four corners should all be around the same level, plus or minus maybe 2 or 3mm (so 4 to 5mm total difference is OK). The level differences across the floor should be in range of about 5mm - if the minimum value is something like -5mm (indicating that the floor is 5mm higher than your laser datum corner) and the maximum is something like +20mm (indicating a low point) then you have a 250 to 25mm downwards bow in the floor. May sound complex, but is doable with a £30 laser and is the fastest, most accurate technique I know and is basically the technique which is used to set raised access joisting

How big should the joists be ideally? What remedial work needs doing if any?

As a rough guide 2in wide C16 structurally rated flooring joists should be at least 1/2in wide for every foot if unsupported span - so a 12ft span requires 6 x 2in, an 8ft span 4 x 2in, a 16ft span 8 x 2in, etc. There are NHBC joist tables on the web which will give you more exact figures, but this is a reasonable basic check

Remedial work normally involves lifting the floor and sistering the existing joists with properly sized C16 (structural grade) joists. Sistering is where the new, straight joist is bolted to the old bowed joist every 600mm or less. If the old joist ends are pocketed into the walls, the new ones should also be pocketed (i.e a pocket is excavated in the masonry, the joist ends inserted and the brickwork around the joist end made good)

Will it fall through or not.

Without lifting a section of the floor next to the wall and examining the joist ends it is impossible to say for certain, but likely not is the answer. One of the good things about nailed timber structures is that they tend mot to faol suddenly and are more likely to suffer a progressive failure if they fail at all (ever seen photos of houses in WWII where the bable end had collapsed, yet the floor, with the joist ends visible, was still hanging there with a bed and eardrobe on top?)

Sorry, long answer, but for an experienced joiner this isn't a difficult job

 

[Shesh222]

Woah thanks for such a detailed response. Really appreciate it. Its one of those things that i didnt know where to start with really. I will have a go at measuring it all as you say and i need to speak to a joiner anyway about something else so ill probs take the floor up and ask them if theyll take it on. Thanks!

 

[Deleted member 174758]

If you are going to use a joiner, why not ask if he'll laser the floor for you? Shouldn't take more than about 30 minutes for someone with a laser