'bouncy' upstairs floors

Robbox

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• 4 Jun 2019

• #1

Now before the jokes start flying, allow me to explain that bouncy is not bouncy as in bouncy castle etc....
In our semi upstairs, the two rooms at the back, a bedroom and the bathroom, both kinda flex when you walk across the floor. Furniture wobbles a bit.
The house is '60's and the joists measure 7 1/2" x 2" and run side to side. Spans in those rooms are 3.6m, but it's the same for the two front rooms (which don't have the same problem)
What is the most likely reason?

 

KenGMac

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• 4 Jun 2019

• #2

Robbox, good evening.

By any chance has someone removed a partition wall under these two upper rooms?

Can you "estimate" the deflection? OK not an easy ask??

Ken

 

Harry Bloomfield

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• 4 Jun 2019

• #3

KenGMac said:

Robbox, good evening.

By any chance has someone removed a partition wall under these two upper rooms?

Can you "estimate" the deflection? OK not an easy ask??

Ken

Click to expand...

Easy way is two poles loosely held together, so the top one touches the floor to ceiling in the room below, with someone to hold them. OP walks across the suspect floor, which will push the upper pole down, gap then between pole and ceiling, will indicate maximum deflection.

 

L

Leofric

• 4 Jun 2019

• #4

Depends on the thickness of floor boarding , spacing of the joists and if there is herringbone strutting between the joists at mid span.

 

Robbox

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• 6 Jun 2019

• #5

We had a partition wall remove this year, but it was like this before the steel went in. I think I will open up some boards and see if there are many cross pieces. I’ve read that 45 degree cross pieces work better.

 

D

Deleted member 174758

• 9 Jun 2019

• #6

Personally I doubt that you'd find herringbone strutting in many 1960s (or later) houses unless they are the stamped metal variety - it simply takes too long to install. It is also going to be a bugger to install if either the ceiling or the floor are in place (because you need good access in order to rebate the tops and bottoms of the joists).

Solid strutting or blocking (often called "noggins" by folk who don't realise the difference) can be retro fitted using a nail gun or cordless screwdriver and with only either the ceiling or the floor out. Rule-of-thumb is that it should ideally be of the same cross section as the original joists, but certainly the same thickness and no less than 80% of the depth (e.g. for 7 x 3in or 170 x 70mm joists that would mean no smaller than about 6 x 3in scant or 140 x 70mm). Either run a row down the middle of the floor or two rows at 1/3 of the way across the floor and don't miss any inter-joist gaps.

BTW just what do you mean by "45 degree cross pieces"?

 

Last edited by a moderator: 9 Jun 2019

L

Leofric

• 9 Jun 2019

• #7

JobAndKnock said:

Personally I doubt that you'd find herringbone strutting in many 1960s (or later) houses unless they are the stamped metal variety - it simply takes too long to install.

Click to expand...

A large housebuilder used timber herringbone strutting in 1997 on my house ,no rebating of joists, just nailed to sides of joists.

 

D

Deleted member 174758

• 9 Jun 2019

• #8

Thanks for that. I have to admit that the last house I built for myself in the late 1980s used metal herringbone and that it required rebating top and bottom. That was what the local builders merchants supplied. Since then the limited number of domestic new builds I've worked on have been either block and beam or corrugated steel and concrete upper floors (with a concrete raft). We still use joisting on some commercials, but it tends to be large section timber with solid strutting specified

 

L

Leofric

• 9 Jun 2019

• #9

I wasn't suggesting using timber herringbone strutting , use the proprietory metal struts.

 

J

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• 11 Jun 2019

• #10

JobAndKnock said:

herringbone strutting [...]It is also going to be a bugger to install if either the ceiling or the floor are in place

Click to expand...

Id second that it'll be the lack of struts causing the issue, or maybe incorrect notching. True that it's a pain to install, our upstairs joists had been notched all over and enough of the struts had been blown away by plumbers (there were 3 sets of heating pipes, only one in use)
My solution with only the floor up was to cut 1m by 7 inch strips of 18mm ply, cut struts from 2 by 3, screw the struts to the ply first bottom edge only, then screw and PU glue the ply to the sides of the joists over the notches. Then only the top edge needed screwing across to make the cross pieces.
Took ages and you're right it was a pain to install, but it made a massive difference to the floor/trampoline.