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Old 02-25-2011, 01:11 AM   #1
mathil
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Default Holes in Load Bearing Cinder Block Walls

Hey All!

Have a question here. I need to install a wall shutter fan (18" 3600 CFM) in my new shop. My question is how do I safely knock a hole that size in the wall? Do I need to cut it oversize and brace it somehow, or is the wall strong enough around it that it won't be a problem?

The other tenants in the complex have done some crazy shit that looks really sketchy, but I'm not that kind of guy...I respect other peoples property too much to not do it properly.

So any help is super appreciated! I did a search but didn't come up with anything. Thanks alot!

Bryan
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Old 02-25-2011, 01:25 AM   #2
IDASHO
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Default Re: Holes in Load Bearing Cinder Block Walls

Are the blocks grouted and reinforced with rebar? or are they hollow?

I wouldnt have a problem with it if they were grouted and reinforced.

If they are hollow, you will need to install a steel header for that size of a hole. 18" is huge. In order to install a header you will have to do some demo, knocking out a few more bricks than you actually need to remove for the fan, install the header, then rebuild.
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Old 02-25-2011, 05:20 AM   #3
Kevin54
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Default Re: Holes in Load Bearing Cinder Block Walls

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Originally Posted by IDASHO View Post
Are the blocks grouted and reinforced with rebar? or are they hollow?

I wouldnt have a problem with it if they were grouted and reinforced.

If they are hollow, you will need to install a steel header for that size of a hole. 18" is huge. In order to install a header you will have to do some demo, knocking out a few more bricks than you actually need to remove for the fan, install the header, then rebuild.
18" is only 2" over the size of a standard block. Standard block length is 16". They put crawlspace vents in all the time (made out of cheap aluminum) without any header, lintel, or such, under a load bearing wall. A steel header would just be overkill.Heck, the opening to my crawlspace is probably 24" x 32" and just uses the house bottom plate and rim joist above it and nothing has ever bowed or moved in 22 years.
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Old 02-25-2011, 05:35 AM   #4
little d
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Default Re: Holes in Load Bearing Cinder Block Walls

mathil, what your wanting to do is done all the time, safely. lay out the hole you need, it will be easyer if you start the top in a grout line but you dont have to. you can rent a gas powered concrete saw and cut the top line 6 to 8 inches past where you lay out the vertical cuts, inside and out. these saws come with a atachment to hook a garden hose to, you will not bealive the difference between using a little water and not! have a metal suplier cut you 2 peices of angle iron to fit into the slots, they should be able to tell you what thickness/ dimentions you need. these are called lintels(spelling?) depending on the grout between the blocks/bricks, you may need to drive them in with a sledge hammer. after these lintels are in you are good to go, the blocks/bricks 6 to 8 inches past the vertical cuts will carry the load. cut the other 3 lines( 2 verticals and bottom) inside and out. knock out the rest of the hole and install. i dont know how the Mfg wants your fan installed but if they want it installed to wood, just alowe for the dimentions of the wood when ya lay it out.

the first time i did this was for a 8 by 8 door in an old 2 story birck building, scared the be-jeasus outa me. it's still there after 20 some-odd years now.
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Old 02-25-2011, 05:37 AM   #5
stafford
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Default Re: Holes in Load Bearing Cinder Block Walls

How many courses of blocks are there above the hole? The more courses there are above the opening you want, the bigger hole you can cut. If you've got 4 or 5 courses, don't worry about it. Make your hole 4" larger and put a 2 x 8 frame inside the hole. put the top peice and bottom in and then cut the sides to fit. nothing to worry about.
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Old 02-25-2011, 05:38 AM   #6
danski0224
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Default Re: Holes in Load Bearing Cinder Block Walls

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Originally Posted by mathil View Post
Hey All!

Have a question here. I need to install a wall shutter fan (18" 3600 CFM) in my new shop. My question is how do I safely knock a hole that size in the wall? Do I need to cut it oversize and brace it somehow, or is the wall strong enough around it that it won't be a problem?
A lintel for a bearing wall is a pretty stout piece of iron. I have usually seen 3" x 4" x 1/2" angle iron. Two pieces are used, with the 3" legs back to back and welded together. enough of the block in the center is cut out to fit over the rise in the middle, or 2.5" depth solid blocks are used to face out the lintel.

I have also seen a piece of 2" x 2" x 1/8" angle used.

I have also seen nothing used as a lintel.

A hole in a bearing wall under something like a roof truss will be treated differently than the same hole between trusses and outside of an imaginary line drawn at a 45* angle from the truss/beam bearing point.

The only way to find out what is proper for your location and application is to check with the building department.

Commercial and residential building standards and codes are usually different in the same municipality.

Last edited by danski0224; 02-25-2011 at 05:41 AM.
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Old 02-25-2011, 06:46 AM   #7
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Default Re: Holes in Load Bearing Cinder Block Walls

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Originally Posted by little d View Post
mathil, what your wanting to do is done all the time, safely. lay out the hole you need, it will be easyer if you start the top in a grout line but you dont have to. you can rent a gas powered concrete saw and cut the top line 6 to 8 inches past where you lay out the vertical cuts, inside and out. these saws come with a atachment to hook a garden hose to, you will not bealive the difference between using a little water and not! have a metal suplier cut you 2 peices of angle iron to fit into the slots, they should be able to tell you what thickness/ dimentions you need. these are called lintels(spelling?) depending on the grout between the blocks/bricks, you may need to drive them in with a sledge hammer. after these lintels are in you are good to go, the blocks/bricks 6 to 8 inches past the vertical cuts will carry the load. cut the other 3 lines( 2 verticals and bottom) inside and out. knock out the rest of the hole and install. i dont know how the Mfg wants your fan installed but if they want it installed to wood, just alowe for the dimentions of the wood when ya lay it out.
+1 this is a proper way to do the install. You can get the correct angle iron and length information from any local brick or block distributor. Also be prepared for a mess if the wall has block insulation(looks like bean bag filler). 3600 CFM is impressive air turn over, how big is your shop? You may need to look into a fresh air intake to allow for good airflow. Just to stop your paperwork from being sucked out
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Old 02-25-2011, 12:20 PM   #8
mathil
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Default Re: Holes in Load Bearing Cinder Block Walls

Hey guys, I'm overwhelmed by the helpful information here!

My shop is 24'x100' by 17' high. The building is a flex space arrangement with beams running lengthwise along the 100' spaced 25' apart. I'll probably end up punching (not literally) 2 holes in my 25' of back wall. That cfm rating gives a shop turnover of about 13 minutes, so I'm thinking of doubling the fans, one in, one out.

Since the roof is 17' high, and the fan is going to be somewhere around head level there are many courses of brick above the planned hole opening. The blocks are empty with nothing inside, and the grout is about 5/16 - 3/8".

I'm a lowly RV manufacturer, so I have all the tools laying around to get the job done. I might even have some heavy angle iron to use as lintels. I haven't bought the fan yet, since I needed to know what is feasible before outlaying the cash. Any idea on steel thickness for the lintels if the grout is that size?

Thanks again guys!
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Old 02-25-2011, 12:32 PM   #9
stafford
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Default Re: Holes in Load Bearing Cinder Block Walls

nothing will happen if you cut that small of a hole in that wall. no need to get the govt. involved.
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