I’m currently renovating an old flint cottage and the floor above the ceiling in the kitchen is sagging so I’ve asked a builder to replace all the joists in that area.
The beams that are currently in there are six inches tall and he is saying that the new joists should be 8 inches tall to spread the load.
I suggested just using more joists to spread the load which he agreed to, but he’s now saying that building regs state that the joists need to be 8 inches high, and I’m trying to find out whether this is accurate.
If the new joists are going to be 2 inches higher than the ones currently in there, I’m going to end up with either a 2 inch higher floor upstairs which means the staircase is going to be too short, or a 2 inch lower ceiling downstairs which will be lower than the ceiling in the rest of the house!
Please can somebody "in the know" tell me if it’s true that I have to use 8 inch joists and it’s stated in the building regs! I’d really appreciate it!
Just to add to this, the reason the floor was sagging is because there were brick partition walls built onto the old floor above without any kind of supports from underneath.
At this stage in the project, there would be nothing at all stopping me from changing from 2×6 to 3×6 or 4×6 etc and still use more beams if it would be okay.
This house is 150 years old - are there a different set of regs for older houses? There is nothing wrong with my house apart from me wanting arrow straight floors and ceilings and it seems crazy that I can’t replace like-for-like but beef it up substantially by using wider beams and more of them, instead of going for fewer 2×8 beams which means I have the knock on effect of a changed floor height upstairs or a changed ceiling height downstairs.
It seems like a ridiculously large problem being caused just for wanting a level ceiling and upstairs floor.
I’m having underfloor heating and thought it would be a good to level up the floor by changing the joists at the same time and thought it would be a simple case of taking out old beams and replacing with new.
Do I really need to get an inspector in for renewing wood?
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Their are old rules of thumb but much better and economical to get a structural chart giving spanning distance, joist spacing and timber dimensions. The main wood companies provide these.
Edit: you can thicken up on the joists so what were 2" can become, say, 3" or even 4" to preserve the ceiling thickness or reduce the joist spacing.
It depends on the room span. The graphs in the Building Regulations book gives you various joists thickness and height against a chart showing span. ie, a 150mm x 50mm joist taking a 1.5 kN/m2 load at 400mm centres will span up to 2.7m and 150mm x 63mm joists will span 3m and 150mm x 75mm will span 3.2m (all SC3 timber)
Useing standard 2×6 lumber, there is a maximun span distance regardless of spacing. I have found that the building inspectors may work with you if you explain the circumstances. You could offer closer spacing and see if he will agree. You could offer to use douglas fir and 12 inch spacing, he worst he can say is no.
He is correct 2×8 is required. Obviously the reason you have to replace them is because the original 2×6’s can’t support the floor above. You could double up as you mentioned,but it will not be approved by a building inspector if you have open building permits and require inspection. Don’t cut corners, the floor is all ready sagging so I don’t understand why you would want to do it wrong again. I would recommend that you drop the ceiling below rather than have an uneven floor above.
Regs would apply differently to new build than to renovation, but did you stop to wonder why they were saggy in the first place?
Speak to someone in Building Regs at the local council. They are generally helpful if you approach them for advice.
USA Per the building code, joist sizes are determined based on the following: The load to be carried, the distance between the joists, and the span of the lumber. The load to be carried is either a living area, such as kitchen, rec room, etc…, or a bedroom. The span is the distance between the two support walls that support the joist. For a residential living area such as a living room, the load is 40 PSF. At 16" on center, a 2 x 6 joist can span a max 9 feet 4 inches. A 2 x 8 joist can span 12 feet 3 inches. If the room above is a bedroom, that is only a 30 PSF load, and at 16" on center, a 2 x 6 can span a max 10 feet 3 inches, and a 2 x 8 a max 13 feet 6 inches.
Note, the above sizes are based on the joists spaced at 16" on center. If you put them closer together, you can increase the loads. For example, at 12" on center, a 2 x 6 for a bedroom can span up to 11 feet 3 inches, which is one foot more than at 16" on center.
I don’t know the size of the room, but I am inclined to believe the builder. If ceiling height is critical, and you REALLY want to stay with 2 x 6 lumber, depending on the span you might have to double the quantity of joists, which would probably cost more than the normal quantity of 2 x 8 joists.
Your local building inspector should be able to show you the charts in the code book that show joist sizes and spans. It is in section 500 of the International Residential Code.
Here’s a link to a Yahoo search for ‘joist span tables’: