View Full Version : This Old House Part III

11-14-2004, 03:59 PM
This place never ceases to amaze me. During the demolition I discovered some space above the third flight of stairs, and crawled up on some shaky rafters for a looksee. Viola! - an entire fourth story of totally unused and inaccessible space, about 30x20x12 at the peak. Amazing. Everyone thought the third-floor ceiling was flush with the roof. From the outside there's no sign. That makes this a 5-story house if you count the basement, somewhere around 4000 square feet.

Gonna rig up some kind of access to this new space, for storage, although it's big enough to be a bedroom or study. There's also about 4 feet above the drop ceiling in the kitchen that could be opened up. New houses don't waste space like this, do they?

This also revives the possibility of a homemade elevator, since it turns out there's plenty of space for a bull wheel at the top. Man, this is even better than fooling with the boat! Just the thing for cold-weather projects.

[ 11-14-2004, 04:02 PM: Message edited by: Victor ]

Boomkin Joe
11-14-2004, 06:54 PM
Check carefully, if there's no skin-on-frame canoe in there you've been robbed!
Checking my ceiling right away. ;)

Bob Smalser
11-14-2004, 09:59 PM
...crawled up on some shaky rafters... They sound more like ceiling joists to me....and unless they are 2X8 or larger on 16" centers and short spans of say, 10-12', you can't do much with that space without reinforcing them with doubling, queen posts or other additional structure.

With none of those joists already doubled and headered for a future access, they were engineered to hold the rafter ends together supporting the total roof load, not to support a floor load across their spans. Heavy, brittle, fragile, terra cotta tiles on the roof?

They are also gonna need solid blocking in each joist bay before laying a floor.

I'd have an experienced framing carpenter (as a minimum...a structural engineer is better) gander at them before making any big plans.

Many older houses were overbuilt by the "engineering of experience", but many also have weak spots structurally that can make ill-planned improvements disastrous.

[ 11-14-2004, 10:13 PM: Message edited by: Bob Smalser ]

11-14-2004, 10:47 PM
Thanks Bob that was useful. Slate roof. So their stress is tensile? What would happen if I cut two of them? The roof could spread? This place is so overbuilt I thought I could get away with it, but it would be prudent to have somebody who knows what he's looking at check it out, if I can find somebody to come.

Roger Cumming
11-14-2004, 11:39 PM
Before you install the homemade elevator let the local rescue squad and the hospital know what you are doing, just in case.... And you may as well find out what your insurance policy has to say about accidental death and dismemberment.

Bob Smalser
11-15-2004, 02:42 AM
Originally posted by Victor:
So their stress is tensile? What would happen if I cut two of them? The roof could spread? Yes....and yes, in the worse case cracking some of that equally-brittle slate with the movement.

Before any access is cut, the joists on either side of the opening must be doubled for their full length, and double headers installed on the cut joist ends to transfer their function to the doubled joists.

In some weak structures....and until your have somebody look at yours, you don't know really know what you have....heavy come-alongs must be used to temporarily hold the rafters inwardly tight while their ceiling joists are being cut for header installation.

You could even have a (arguably weaker but definitely touchier) balloon as opposed to a platform frame which makes all I've said in your three "House" posts even more important.

[ 11-15-2004, 03:09 AM: Message edited by: Bob Smalser ]

11-17-2004, 06:51 PM
Ceiling joists are 2x8 (REAL 2x8s), 24" on center. Floor joists are also 2x8s, 18" on center.

Bob Smalser
11-17-2004, 07:15 PM
2X8X24 passes no codes here. The difference 'tween 2X8 true and 2X8 nominal ( 1 1/2 X 7 1/2) doesn't equal a 2X10 by a long shot.

Gotta be 2X8X16.

It's workable with light attic loads, but it's no place for a barn dance or that hot tub.

11-17-2004, 07:32 PM
Actually it would just be storage if anything at all. OK to put some plywood up there and walk around?

Bob Smalser
11-17-2004, 08:04 PM

Just don't cut any without doing what I said.

11-20-2004, 07:12 PM
What's the difference between balloon and platform frame?

The two joists I want to cut are about 19 feet long. How would I attach them to the adjacent ones?

Bob Smalser
11-21-2004, 02:18 AM
Originally posted by Victor:
What's the difference between balloon and platform frame?

The two joists I want to cut are about 19 feet long. How would I attach them to the adjacent ones?In balloon frames the studs run from the foundation sill all the way up to the top plate beneath the rafter birdsmouths and the upper floor joists are hung from them.

In platforn frame each floor's studs have a top plate and the headered joists of the floor above rest on that top plate.

24" OC 2X8 is weak enuf that to cut two of them, I'd sister the outer joists of the opening on their outside faces the entire 19' span....nailing them both to the rafter pair and to the joist they are mated to with nails spread out so there is no more than a 6" or so circle without a nail in it. Or better yet, go getcha a framing or local code booklet with a nailing schedule in it, as mine is out at the shop right now.

Then because of the slate roof I'd lag bolt a 2X8 cleat to the two rafter pairs you are gonna cut the ceiling joists of...on both sides. Then I'd put a comealong and straps on them and pull them up fairly snug.

Then I'd cut and header the two ceiling joists of your opening on both ends....using a double header on each nailed both to the outside doubled joists and the crippled joists. Then and only then would I remove the comealong.

For a 19' span, I'd cut solid blocking and nail that into each joist bay 6' from the ends....two in each bay. Then and only then would I lay a plywood floor.

11-21-2004, 07:31 AM
Thanks Bob.

11-24-2004, 05:19 PM
Hey Bob, how bout running stringers between the rafters above the cut joists?

Bob Smalser
11-24-2004, 06:52 PM
Originally posted by Victor:
Hey Bob, how bout running stringers between the rafters above the cut joists?Stringer? As in crossways to the rafters? Wouldn't do much, as wood isn't stiff in that direction. They're called purlins and they are mounted on posts to support the vertical load of the rafters....the posts do the work.

Beefing up the collar ties would be better if they are puny little triangles at each peak....a 2X6 as low as you can get it and still have headroom is good.

[ 11-24-2004, 06:54 PM: Message edited by: Bob Smalser ]

11-24-2004, 07:00 PM
I guess stringer is not the word. I meant parallel to the joists, but higher up.

Bob Smalser
11-24-2004, 07:05 PM

Collar ties do that work...the load is downward and, accordingly, outward along the slope, trying to push the walls apart. The structure of plates, ceiling joists and collar ties supporting the rafters is there to hold them up and in.

Rafters only need to be doubled around openings such as dormers....and that's mostly for nailing surface. Doubling them partially without providing a birdsmouth to support the double's share of the load could even easily be harmful, as it hampers rather than supports the rafter's ability to resist bending stress.

[ 11-24-2004, 07:09 PM: Message edited by: Bob Smalser ]

11-24-2004, 08:14 PM