Concrete walls on wooden joists - DIY Chatroom

stonehanger · 11-24-2006, 04:52 PM

We have just moved in to a new house (built 1955) and we have discovered that the interior walls are breeze block (17" x 4" cement blocks). Very heavy. No problem downstairs on concrete floors but we were astonished to find that the upstairs dividing walls are built directly on 7" x 2" wooden joists with no load-bearing walls below them, in fact nothing below them. I calculate the longest wall is around 1350kg over 2.7 m which is a load of 500kg per metre over two thirds the joist length. I think this is way too much for the joists but my husband thinks there is nothing to worry about. Any thoughts?

concretemasonry · 11-24-2006, 06:01 PM

Since you refer to "breeze blocks" you may be from the U.K. or the Appalachian (sp?) area of the U.S.

Are the breeze block mortared or are they just plastered for an interior non-bearing wall? If plastered, they may be just a dead load (mass) and not a bearing wall. This application is used frequently to provide internal thermal mass and minimize the a mount of heating capacity required.

If the block are mortared, the span is very short in comparison to the wall height above and there could really be very little load on the joist due to the "arch action" of a masonry wall.

I suggest you contact a local engineer to see what the entire structural configuration consists of and how everything works together.

Since your description does not fit the stereotype U.S. condition of construction, which is not the same as the majority of the developed world, you need local advice on your condition.

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stonehanger · 11-24-2006, 06:15 PM

Thanks for the reply. Yes, we are in the UK. The blocks are mortared. We have taken down one wall that was separating a bathroom and toilet, it was sitting directly on the floorboards over the joist and came down fairly easily. It was doing nothing to support the ceiling joists above (there was a gap). If the dividing walls were supported at each end by a load-bearing wall below I wouldn't be so concerned, but the walls are not keyed in to the exterior wall and they extend only part way along the length of the joist therefore loading it unevenly.

concretemasonry · 11-24-2006, 06:26 PM

You observed and removed a wall that was not loadbearing.

Trial and error is not the best way to find out what consequences there are when you remove a wall.

The fact that the walls were not keyed into each other is usually not critical, but it is important in the big picture.

The U.S. approach (limited structurally) is to stack up things and not be that concerned with the interaction of portions of a structure. Your home was not built that way, so you would be well advised to look to a professional in your area that is a little beyond the "stack up" lightweight construction philosophy. Your home may well be adequate or actually beyond the performance of someone not familiar with that type of construction.