Hello!
I've framed a new floor structure with 45x220 joists at cc60 with a span of 3.70 m and plan to have a 25mm wooden floor in the room, but should I use subflooring first or is it okay to screw directly into the joists without the floor becoming wobbly? Glued and screwed chipboard with 45x220 should handle a span of 4.14 m whereas just the regular floor should handle 3.44 m. How have you others done it?
I've framed a new floor structure with 45x220 joists at cc60 with a span of 3.70 m and plan to have a 25mm wooden floor in the room, but should I use subflooring first or is it okay to screw directly into the joists without the floor becoming wobbly? Glued and screwed chipboard with 45x220 should handle a span of 4.14 m whereas just the regular floor should handle 3.44 m. How have you others done it?
I had screwed the wooden floor directly onto the joists
It is best if you use screwed plywood flooring first. Otherwise, the floor deflection will be too great. Then you can use thinner floorboards instead.
Thanks for the response, yes maybe it's better not to take a chance and go with floor chipboard first. Does anyone know where to find thinner, wider solid wood flooring? I've seen 14 mm, but only just over 12 cm wide. I would have liked floorboards 16-18 cm wide at least 
There are wider 14 mm floors than 120 mm. Just Google "thin solid wood floors" or something similar. Otherwise, you can always order it from a custom carpentry.
Thanks for the response, I'll have to look around a bit, on the other hand, it's not a problem if the floor is slightly more than 20mm, so it should work out
Another question: The house, which is currently an uninsulated shell without intermediate floors, is impossible to heat up for the time being. If you want to screw and glue particle board now or in the near future, how warm should it "at least" be to get a good result? Winter glue states that it can be used down to -10 degrees, is this really accurate? I'm thinking it should get a few degrees above freezing here next week, is it safe to lay it then? Or is it wiser to wait?
Another question: The house, which is currently an uninsulated shell without intermediate floors, is impossible to heat up for the time being. If you want to screw and glue particle board now or in the near future, how warm should it "at least" be to get a good result? Winter glue states that it can be used down to -10 degrees, is this really accurate? I'm thinking it should get a few degrees above freezing here next week, is it safe to lay it then? Or is it wiser to wait?
Winter adhesive works reliably. However, you should be mindful of the different materials' moisture levels. Fresh wood, in particular, may have a higher moisture content compared to particle boards. This can result in unwanted movement between the materials. Floorboards, which are often very dry and wrapped in plastic, should not be handled until you have room temperature indoors.
Thanks for the reply, yes maybe we'll wait until spring for the actual floor chipboard then. It is regular C24 45x220 from AB Karl Hedin, and it maintains a 16% moisture ratio according to them, and I assume the floor chipboard might maintain around 7-8%?
That is probably quite accurate. Especially the floor joists will dry out. The movements that occur are primarily in the radial direction. It is wise to wait until spring with the floor chipboard.grasfield said:
In addition to concerns about deflection, it might be good to consider future sanding. We have laid solid pine flooring on floor chipboard and initially thought about going with a 14 mm floor. However, we were advised by the supplier to go with 20 mm, as the thinner one can only "withstand" one sanding; after that, you sand down to the chipboard. 20 mm should withstand at least two rounds.
Thanks for the response! Yes, as mentioned, the thicker wooden floor doesn't matter at all really, maybe rather an advantage as you write Bernieberg.
I was thinking more about subfloor on new wooden joists, how do they build new houses in winter? I think it might be an advantage to lay it now because the humidity is supposedly highest in summer and fall and lowest in spring and winter? I figure if the humidity in the air increases, the wood "grows" and if the humidity decreases, it shrinks? Or am I thinking wrong?
If you read various installation instructions for subfloors, including this one, they seem to account for the joists shrinking after the subfloor is laid: https://np.netpublicator.com/np/n16990392/Golvspån_contifloor_monteringsanvisning-.pdf
On page 3 under point 9 it states:
The screws should be countersunk about 2 mm into the board. The screw countersink
should not be filled as this may cause markings in the
floor covering in the form of small elevations when the joists have dried out.
Of course, we will do what is best, but if the flooring (at least the subfloor) doesn't arrive until spring, the construction will halt at many points, which would be very, very disappointing!
I was thinking more about subfloor on new wooden joists, how do they build new houses in winter? I think it might be an advantage to lay it now because the humidity is supposedly highest in summer and fall and lowest in spring and winter? I figure if the humidity in the air increases, the wood "grows" and if the humidity decreases, it shrinks? Or am I thinking wrong?
If you read various installation instructions for subfloors, including this one, they seem to account for the joists shrinking after the subfloor is laid: https://np.netpublicator.com/np/n16990392/Golvspån_contifloor_monteringsanvisning-.pdf
On page 3 under point 9 it states:
The screws should be countersunk about 2 mm into the board. The screw countersink
should not be filled as this may cause markings in the
floor covering in the form of small elevations when the joists have dried out.
Of course, we will do what is best, but if the flooring (at least the subfloor) doesn't arrive until spring, the construction will halt at many points, which would be very, very disappointing!
Your reasoning regarding humidity is correct, but when it comes to wood, fresh timber starts at a much higher level in terms of moisture content which it never returns to afterward. If you follow the manufacturers' instructions, it will surely work out fine.
Firstly,.. again How about the choice of material for the subfloor? Thinking about span and deflection/stability? One might think that if you have solid wood in the form of, for example, 20x120 rough tongue and groove where each "piece" is screwed into, for instance, a 21x120 raw plane that is attached under a 45x220 floor joist, it should stabilize the floor more than laying an asfaboard or a thinner masonite board, right? It should also help with the cross-bracing together with the upper floor, shouldn't it? You often read about which type of upper floor might be good for the purpose and that cross-bracing/blocking can help, but it's rare to read about whether the subfloor can have any significance in all of this. Surely there should be a difference in the type of subfloor you choose if we're only talking about span, deflection, and stability?
How about the choice of material for the subfloor? Thinking about span and deflection/stability? One might think that if you have solid wood in the form of, for example, 20x120 rough tongue and groove where each "piece" is screwed into, for instance, a 21x120 raw plane that is attached under a 45x220 floor joist, it should stabilize the floor more than laying an asfaboard or a thinner masonite board, right? It should also help with the cross-bracing together with the upper floor, shouldn't it? You often read about which type of upper floor might be good for the purpose and that cross-bracing/blocking can help, but it's rare to read about whether the subfloor can have any significance in all of this. Surely there should be a difference in the type of subfloor you choose if we're only talking about span, deflection, and stability?The geometric property that is significant for both deflection and bending is called the moment of inertia. It is calculated using the formula: the width times the height cubed divided by twelve. This means that the cross-sectional area based on height has the greatest effect. For the subfloor or ceiling to work together with the floor joists, they must be screwed and glued. Blocking and nogging can affect the impact of point loads by distributing them to adjacent joists. However, they can never reduce a deflection.
You see what you learn! Thank you so much for the response!!
Thank you so much for the response!!