reno causing floor boards to buckle?

[gilliang]

Several months ago, we had the floorplan on the second story of a 1920 2 story home altered to:

1) remove a one non-load bearing wall (one of two that make up the bank of closets between 2 bedrooms) to make the master bedroom larger. The perpendicular dividing wall between the 2 closets of 1.75' was left standing, attached to the remaining dividing wall.

2) cut a 4'w x 6.5'h pass through an exterior wall to join the master badroom to the second story back porch. (Proper reinforcing with a doubled beam and cripple studs, and a secondary support studs added on each side of the opening.)

3) enlarge the existing doorframe to the bathroom on a secondary support wall by 1.5'. Again,beams are in place ,etc. The main structural wall that runs parallel (3' over in the center of the structure) was not touched.

4) THE BIGGIE: The ceiling height in the main staircase was only 5.5', due to a previous (perhaps an addendum to the original construction?) addition of floor space to the bedroom over the stairs of approximately 2.5'. There was a danger of people constantly banging their heads, and this severely limited what furniture could be moved upstairs.

The floorspace was cut back out of the bedroom, and one section of joist (4'over the stair to the exterior wall) was removed. The lateral beam along the side of the staircase was tripled, and the cut joist was connected to this with a joist hanger.

This tripled beam continues to the next fully cantilevered joist which was also tripled in thickness over the staircase, the reinforced section spanning from the exterior wall to rest over the main support wall. All the ceiling and floor joists are cantilevered, running the full span of the house, 25', except in the main staircase area.

PROBLEM:

This work was done in February, and I waited until the last 2 weeks in May to have the walls put back in, to ensure that everything was fine structurally after the changes. No cracks in the plaster, no problems in evidence at all.

However, on Friday I noticed a small section of hardwood floor in the second floor bedroom over the stairs, where 2 boards are buckling together, raising approximately .25" on the join. This doesn't run the length of the floor, it is only these 2 boards, the buckling between them occurring for about 3'. There is also a small crack in the ceiling of the living room where the reinforced section of the joist is sitting. (The living room is on the other side of the support wall from the entrance hall/staircase.)

We just experienced very heavy rains, and there was prolonged water leakage into the basement. We live in an area which has a very heavy clay soil composition. This, combined with extremes in temperature fluctuation from winter(-30 C.) to summer (+ 30 C.) makes foundation settlment / some cracks are a fact of life for everyone who lives here in Winnipeg (MB, Canada).

COMMENT:

It seems that the contractors did all the right things, and we hadn't experienced any problems prior to the change in soil moisture. The house is old, but very solidly built, the exterior walls are 2x4 construction, with 1x8 tongue and groove cedar cladding both sides of the studs. Extremely thick and solid.

QUESTION:

Is this just the house settling in to it's new 'shape'? Do I need to be concerned that my house is unsafe? Am I going to have to rip out all the very expensive plaster repairs to get back at the structure? What should I be looking for to indicate that the problem is serious? Are there any tests I can do (walls/floors are level, plumb, etc.) to tell if it is a concern?

PLEASE ANSWER...and please try to give me some good news!

gilliang

 

[Aton]

gilliang, on the surface of things, it does not sound as if you have anything BIG to worry about (with the usual engineer's disclaimer, etc, etc, and without seeing the job!). It would seem as if you did the structural engineering, and your carpenter carried out your instructions. I, too, am a Canadian structural engineer, but I have had the good fortune to have spent the first 25 years of my working life as a carpenter/renovator/designer in Quebec and NS. It may be that your moisture fluctuations, coupled with the change in the way air moves around your house, may have a lot to do with the warping of the floor boards. Without humidification, indoor air is extremely dry in our winters (relative humidity theory). This is the case with air-tight houses equipped with HRVs, or older "leaky" houses with no HRV's (only air-tight houses with no HRVs experience high indoor RH) in winters. Then comes the sommer, with its natural humnidity -- in your case coupled with perhaps increased foundation moisture due to leaking foundations -- can cause wood to swell.

This may explain the 36 inch "buckling together" floor boards, and the crack in the ceiling where the reinforced section of joist is sitting. The floorboards may be swelling, and crushing against each other (I have seen an entire hardwood floor do this, looking like waves on a pool), and the newly-built-up wood joist may also be swelling, causing gyproc cracks to form.

As far as structural damage is concerned, I wouldn't worry, by the sounds of it. Your house has certainly stood the test of time. I have worked in many heritage houses with inadequate footings (built years before Terzaghi, Peck, and Meyerhoff!), and they are still standing. In fact, my owin offices are in an old commercial building first erected in 1861. It is 50 feet long, and is built with its back to a river. Over the years, one of its back corners has dropped 7" from the front diagonal. Yet, aside from some innovative desk-shimming techniques that ate needed, there is no worry that it will collapse.

Monitor the situation over time, but I think you will be OK. This is not much "help", other than a friendly, "Don't panic" message. Good luck.
Sustainable, Solar, Environmental, and Structural Engineering: Appropriate technologies for a planet in stress.

 

[Ron]

Gilliang...I would agree with Aton. You might want to confirm this by cutting a very narrow space for relief at the buckling to see if it settles down, or if it transfers the buckling issue to another location. If the location of this buckling is perpendicular to the joist span, you might want to check the joist deflection. If it is parallel to the joist span, it is clearly a moisture issue.

As for the crack at the ceiling, you have the opposite problem! This is likely due to normal shrinkage of construction materials after placement in conditioned space, particularly heated space.

 

[gilliang]

Thank you Aton & Ron.

FYI:
The floorboards are perpendicular to the joists. Could you please expand on what you mean by "joist deflection". What would be the course of action to take if this is the cause of the buckling? (Which, by the way, has not subsided, and has come up in another span approximately 18" from the original.)

As a further point of reference- these areas, when stepped on, are able to lie flat, and there is no cracking in the walls.

gillian (g)

 

[Ron]

gilliang...
Assuming the joist is support on each of its ends (simple span), joist deflection is when the center of the span of the joist moves downward, either under dead load (the weight of the joist and all materials it permanently supports), live load (temporary loading such as people walking on the floor), or both. This is essentially the amount of "sag" in the joist. If it is cantilevered, the "free" end of the joist will move downward under load more than the center of the cantilevered section.

For the simple span condition, when the joist sags, the bottom of the joist is stretched while the top of the joist is compressed. Anything attached to the bottom will be pulled, while anything attached to the top (such as your flooring material) will be pushed together. You can check this by pulling a stringline from bearing point-to-bearing point of the joist and measuring any gap between the string and the floor surface. For each 10 feet of span, this amount should not exceed about 1/2-inch.

Based on your description, it appears your problem is more likely attributable to moisture gain (swelling) or perhaps (though less likely) some longer term "creep" or natural deflection of the joists under continuous load.