Ask Me Help Desk - Sister unsupported rafters

My house has a 10 x 20 porch off the master bedroom that someone in the 50's - 60's decided they were going to finish off into useable space. They never finished. So, now I have a really poorly made roof and some walls with really poorly installed windows.

I have the intention of finishing this space, but first I need to fix the sagging roof. Here is a breakdown on the roof construction:

It consists of 2x4 rafters that are about 16-20' long. They are only supported on the exterior walls and the ridgeplate. The rafters are set about 20" apart running the 10' distance.

As you can imagine, the roof is sagging.

All the research points to using sister rafters, but I am wondering if I should be using 2x6 or 2x8 sisters and should I just sister each rafter once or on both sides of the rafter? Or should I be trying to install new rafters and bring everything into 16OC alignment?

Secondly, regardless of what size lumber I need, should I notch the end of the sister rafter that will rest on the topplate of the exterior wall, otherwise it will not fit?

Third, should I add collar ties?

Forth, My wife wants me to keep as much of the ceiling vaulted as possible. Will a sister rafter roof support the weight of the roof and sheetrock or am I going to have to put in a normal ceiling?

Thanks.

If u cut the birds mouth (part that sits on top of wall) to the depth of a 2x4, u will defeat the purpose of larger rafters.

Birds mouth should be cut width of wall top plate. If wall is 2x4 studding, then birds mouth would be 3.5''.

On a 20' span, rafters can be 2x6 if pitch is higher than 8''.

For the collar ties use 2 (one each side) 0n every third rafter.

Old roof should come down.

Chuck

Quote:

Originally Posted by creahands

If u cut the birds mouth (part that sits on top of wall) to the depth of a 2x4, u will defeat the purpose of larger rafters.

I was planning on bringing the walls from a 2x4 depth to a 2x6 depth for insulation purposes. What if I cut the birds mouth so part of the rafter sits on the top plate and the remainder sits on the expanded wall joist?

Quote:

Originally Posted by creahands

Old roof should come down.

Really? I have had two contractors (one provided by my city, Minneapolis) tell me the roof doesn't need to come off. Can you explain why you think the roof should come off? If I were to take the roof off I might as well replace the walls also.

Thanks

The pitch of the roof would determine if roof would have to come down.

Also the amount of deflection of rafters has to be considered. If existing rafters are sagging too much, will not be able to reverse sag.

The more u cut out for birds mouth the weaker the rafter.

Let us know pitch of roof so can better advise.
Also amount of rafter deflection.

My opinion is derived from your info.

Chuck

Ebne. I see a different picture here. If the rafters there is already bowed at that length they are worthless. So is the ply and roof above. If you are thinking of sistering to the old joist the deflection on them will or may control the birds mouth cut to drop the new rafter down far enough below old rafter to get away from that deflection ( as crehands also mentioned ) if this ceiling is now "vaulted" Basic birds mouths are cut in depth 1 1/2" and set on a double top plate which still leaves a nailer for drywall at the top.

That being said I see your Geo. You should be min (R 19) insul 9" thick with a bafflein rafters at the low slope end and soffit are up the rake to vent to complete the venting.

So lets think of what's needed in depth to insul which controls the roof rafter thickness on a low slope roof, which in turn really beefs up the roof rafter to the point that size/height of rafter is usually moot.

Quote:

tell me the roof doesn't need to come off. Can you explain why you think the roof should come off? If I were to take the roof off I might as well replace the walls also.

Ignore them they don't know that they are talking about. To fool with that bowed roof and try to flatten it out is a serious waste in manpower. A sawzall and crow bar and the roofs gone in a matter of hours. Now it's a clean slate. I see where this is going of why stop there. The only reason I can think of is the grandfather clause in old codes to new. They way we get around that is leave one wall up. Attach new walls to that and now its back to a structure. The we add/pull a permit to add the 4th wall new. They hate it buts is legal here in terminology of " structure new verses renovation permit. Just a FYI here.

So bottom line here is forgot the old roof completely. Order some 2x12s 20' set at 16"oc or 12"ocl( depending on building code there and put in a vaulted ceiling. Now you have space for R value and its now an inside ceiling "Vaulted which makes the 10 wide room look less skinny/hallway look. Use rubber for the roof and have well built/insulated structure.

You can rip some 2bys down and scab onto the inside of the exterior walls and get the insul depth that way. Now if the façade is rough then I would tear it down to sub floor and new 2x6s and new windows sizes you like and tilt in to clean easier. AMAZING how it goes from a bowed roof to a full blown addition excluding the floor. MY motto is if you start with junk then you end up half still being junk. Obviously there is nothing of real value there to save/
1. Roof needs completely replaced
2. Walls not thick enough for insul ( although spray foam can get better (R) value then fiberglass)
2. Windows are junk
Only thing left here is added façade costs.

So, I did some checking and I was off on a few points:

1. the rafters are a little over 16oc. The walls are the 24oc.

2. The rafters are more like 15' long.

I have added a few pics to look at:

http://www.flickr.com/photos/47367104@N00/3726175173/

http://www.flickr.com/photos/47367104@N00/3726175255/

http://www.flickr.com/photos/47367104@N00/3726981428/

From what I'm looking at it's a tear down. The roof also pushed out the exterior wall form what I see. Amazing all the cripple jacks under the window and not any collar beams at the peaks. Its one of those keep throwing lumber at it and still the forces there are for a bad roof load. Not to be unkind you are trying to save a big shed. The 2x4 rafters are not going to allow you to sister a bigger rafter simply there's no room from the plate to the underside of the roof to seat a sister rafter of usable size. Wait until you string line and check the bow from perk to outer plate. You will end up trying to build a roof under a roof and setting another ridge beam to get a straight line to still use the top of the outer plate.

The wide roof planking could be a reuse. Can be used to fill gable in from the top plate to peak. Or a rustic look from chair rail height to floor. They can also be milled/planed down at a real lumber yard and used a rustic Wayne's coat. I have recycled roof planking. Actually laid the boards on saw horses and re warped them back to a manageable flat. I would definitely go vaulted there to make it a big room look

I agree with 21 boat

This is a tear out.

From the looks of the pitch, recommend 2x8 rafters and collar tie every rafter. Set collar ties 1/3rd down from ridge to top plate.

Chuck

I think everyone is right that this is a tear. When looking at the cost, I don't see a huge difference.

But I have a concern with the tear out. This would make this an addition and not a renovation in the city of minneapolis. I am concerned they are not going to be happy with the foundation the addition is being built on as it is not a full basement. Is it possible I am going to have to keep the walls or something strange like that?

Thanks

What is supporting porch? Is bottom of porch closed in?

Looking closer at pictures, it appears that there is no header above windows. Just the double 2x4 plate. It should be double 2x10.

If u pull a permit to do this work, u will probably have to take walls down also.

Chuck

Here is a quick history of the house. Main house was built around 1890-1906. No one know for sure because the area of minneapolis it is located in was annexed in 1906 so all houses are listed as built in 1906. The main house foundatation is a full basement of rough limestone walls 3 feet thick.
The porch that is now enclosed was originally an open porch over a first floor addition, probably in the early 1900's when water/sewer was extended to the house. The first floor addition foundation has a crawl space and it is also a rough style limestone(but more finished the main house). The first floor addition space holds the bathroom, a mud room and a small office/den. I do not know how far into the ground the foundation extends and that is what I am worried about; that the city will want to know this or say they don't believe the foundation will support the weight.
Are my concerns valid?

If the city says the foundation is not strong enough, they will make u tear down the walls and roof.

Not being from your area, can not state that they will accept what u have. If u are not having problems with the addition inside walls cracking it's a good sign that foundation is below frost line.

To alleviate your concerns, dig hole at wall and see how far down it goes.

Chuck