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I have a 100+ year old house with wooden floors.

At the moment, access to the subfloor is difficult, involving a long 25 meter crawl under the deck.

I'd like to install a manhole in the floor. Is this difficult?

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2 Answers 2

up vote 13 down vote accepted

There are several issues here to deal with that I see.

First, you need to find an appropriate location for this aperture. It is best if the location is one that you can get to easily, but out of the way - since a hole in the floor might be unsightly or something to trip over. It also needs to be accessible from below to get in and out. I would suggest a back hallway or back bedroom as being good.

Second, you need to worry about which joists are involved. Can you get through a hole between the joists in your house? If you needed to cut through a supporting beam, this can have very serious and negative consequences on the structure of your house. Do NOT do that without knowing what and where you are cutting, and providing the necessary support for anything that is cut.

You will need to carefully mark out the cut lines. Careful measurements will be important. You may choose to make a tiny hole or two with a small drill bit to figure exactly where you will cut relative to any joists.

Last, the actual work. Cutting through the floorboards, once they are carefully marked, requires no more than use of a handheld circular saw or a reciprocating saw. There are several other types of saw that could do such a cut on the market, rotory "zip" tools for example, even a hand held manual saw if your skills were adequate. If you needed to cut a beam, then you will need to provide new support points for that joist on either side of the cut that are FULLY capable of carrying the load. You may even need to reinforce the floor boards themselves as they were cut on either side too.

To close it all up, take the flooring that you cut out, and create a door from the flooring itself that matches the hole you just cut out. Recognize that this will be a trip point, so do not put a big, bulky handle on it. A simple, low piece of moulding around the perimeter may be sufficient to hide the cuts and support the "door". Even that is a trip point, so be careful here.

All in all, this MAY be something that is best given to a reputable contractor to solve for you if you don't know how to solve the problems that will arise. The cost would depend upon whether you can find a location that does not require the cutting of any beams.

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If you have a closet available to put the hole in, that would probably be the best place for it. Both to avoid a tripping hazard and to minimize the "unsightlyness" of it. You could probably put a floor mat or rug over it as well. –  Eric Petroelje Sep 27 '10 at 19:08
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Somehow I think that to be massive overkill. From the original comments, this is a hole into a CRAWL SPACE, not even a full basement. And access will be made on an infrequent basis. If this is something to worry about, buy an orange traffic cone. When one goes down into the hole, put the traffic cone in front of the closet, in addition to the verbal warning I said I would issue. –  user558 Sep 30 '10 at 9:24
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Or perhaps (tongue carefully placed in cheek), one could install a pressure sensitive pad in front of the closet. When the door into the floor is opened, a switch is thrown. Anyone stepping on the pressure sensitive pad would trigger an audio alarm, speaking the words "PLEASE STEP AWAY FROM THE CLOSET", as well as strobe lights. A siren would then start if pressure is still felt on the pad, and the police and ambulance automatically called in after a specified time. While this is clearly ridiculous, my point is that one can get carried away with things. –  user558 Sep 30 '10 at 9:34
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You TOTALLY need to put it under the woodburning stove like they did in 'great escape' –  Trout Jan 29 '12 at 21:06
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No. It needs to be button activated, in the middle of the room, hinging down. Then you can fill the crawlspace with water and sharks with frickin' lasers. –  Chris Cudmore Sep 14 '12 at 18:31
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The house I grew up in had a manhole to the crawlspace in the utility room. It was actually located under the dryer.

It was nothing special, just a piece of plywood with some flooring on top to match the rest of the room. It was supported below by a 2x4 frame that was attached to the floor joists.

To open it we stuck a table knife into the joint and pried it up.

Our house was built in the 40s, and was nothing out of the ordinary. As long as the floor joists were supported well you should be able to just cut a hole in the floor and make a frame and cover for the hole. I would locate it out of the way, but not under the dryer if possile.

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