reinforcement of sagging joists

[Mekstr]

We have a sagging floor that we are going to reinforce. We have now started breaking up the floor to see how it is constructed. The room is 5.3 x 3.5 m. The joists are 160x68mm and are placed lengthwise in the room. cc~500mm.

The idea is to place new joists on top of the existing ones and reinforce with a couple of rows of cleats. Then screw and glue chipboard. The chipboard will be notched for underfloor heating.

According to this table:
https://www.traguiden.se/konstrukti...-av-fanertra-i-ett-fack/?previousState=001000
45×300 is suggested for a 5 m span. I find it difficult to fit such high joists.

My thought is to splice on 170 or 145 joists. Either one on each side or one per existing joist. How do you approach dimensioning this?

 

[Tompafix]

We have a sagging floor that we are going to reinforce. Now we have started to break up the floor to see how it is constructed. The room is 5.3 x 3.5 m. The joists are 160x68mm and are placed lengthwise in the room. cc~500mm.

The idea is to install new joists on top of the existing ones and reinforce with a couple of rows of noggins. Then screw and glue the chipboard flooring. The chipboard will have recesses for underfloor heating.

According to this table:
[link]
45×300 is suggested for a 5 m span. It is difficult for me to fit such high joists.

My thought is to splice on 170 or 145 joists. Either one on each side or one per existing joist. How do you think when designing this?

Is there a wall underneath? Is it part of a truss? Pictures

 

[Mekstr]

It is a room below that we do not want to partition, as we have the projector there. No wall, but the studs are supported at the ends. The studs are 5.3m. So it is an intermediate floor.

 

[MattEri]

In your case, use the largest dimension you can fit without changing the floor height, 170 or 145 will work excellently, glue generously with wood glue and screw with 6x90 screws at 60 centers, of course, the beams should also be at 60 centers. At your distances, use 4 rows of noggings. And glue the chipboard well, don't skimp. Then it's just a matter of booking rave parties in there. It will never give way.

 

[Mekstr]

There is a room underneath that we don't want to divide, as we have the projector there. No wall, but the joists are supported at the ends. The joists are 5.3m. It is thus a mid-floor.

Here is a picture for the alternative of a joist on each side, as clarification.

 

[Mekstr]

Here comes an image for the option of a rule on each side, for clarification

And the option of only one rule

 

[Mekstr]

In your case, use the thickest dimension that fits without changing the floor height, 170 or 145 works great, glue generously with wood glue and screw with 6x90 screws at cc 60, of course, the beams should also be at cc 60. For your distances, use 4 rows of kotlingar. And glue the chipboard well, don't skimp. Then you can just book rave parties in there. It will never give way.

now the beams are cc ~50, will that be a problem later when the chipboard is laid?

 

[justusandersson]

By screwing and gluing new joists from the sides, you increase the moment of inertia of the beams and thereby the beams' stiffness. To achieve acceptable deflection, you would need to reinforce each beam with two 45x195 C 24 joists. Together with screw-glued particle board, the floor will have sufficient stiffness. If you can find wood in a higher strength class, C 30 or C 35, it will be even better. An alternative is to place glulam beams between the existing beams and let the glulam bear the load. 140x180 could suffice. There are more variations. I recommend calculating it first. Trial and error is not suitable in such a context. Note that short braces can help distribute point loads so that deflection decreases, but they do not increase the overall load-bearing capacity of the floor.

 

[Mekstr]

Thank you for your response. I took 145 on each side and 3 rows of kottlingar. It seems stable.