drilling hole in cinder block load bearing wall?

[Aaron]

I need to drill a small 1" passthru in a roughly 7' X 10' load bearing wall, will this hurt anything?

[Chris Lewis]

According to Aaron :

No. If the voids in the cinder block are filled with concrete and/or rebar, it could be rather difficult. But that's rather unlikely. You want to drill through a hollow. You probably don't want to shatter the block (mostly from an esthetic perspective), so don't get too violent with a hammer drill.

I've watched electricians punch holes in foundation cinder block using hand sledges. This is for installing 2" PVC conduit for service entrances, and the irregularities in the hole will be hidden by the fittings and hole sealant. Surprisingly neat holes tho.

[gfretwell]

You can usually find the hollow cores with a tube up to your ear and against the wall and tapping wiuth the handle of a screwdriver. A paper towel roll or a short PVC pipe works. Dowelled cells are usually in the corners and next to windows and doors. You will also have them about every 4' if there isn't a window or door. The top 2 courses of block will be solid. (coastal buildiing code).

[Aaron]

Thanks, I was worried about disturbing the integrity of the wall itself but I didn't know at what point (from a structural) point of view you could do this. I am assuming if you punched too many holes or too large of a hole that at some point cracks would appear and you would disturb the integrity of the wall?

[HeyBub]

No, the crack would stop at the next course of blocks. You could probably remove every other block and the wall would be okay. Come to think on it, I've seen walls done that way: a checker-board with blocks and spaces. Evidently it works.

[Michael Daly]

Clearly removing blocks from a wall will reduce its strength. The question is whether the reduction it too severe. If the wall is much stronger than it needs to be, removing some of the blocks will maintain enough strength. However, if the wall is _just_ strong enough, removing even one block may have a deleterious effect.

A small hole will have a small effect on the strength - the material in the block will transfer the stresses around the hole. Too big a hole and the block is seriously weakened.

Somewhere in the standards for these blocks you'll find a reference for how many holes can be tolerated with negligible loss of integrity. I don't have a copy of such a standard on hand - try the web.

Mike