Another Mansard Roof question

[andydiy]

Google helped me get here today :)

Here is a summary of our house's issues: During the winter we pay a fortune to heat the house (over $500 a month for 2520 sq ft). We have hot water heat and a brand new furnace, so should not have any issues with that. During the summer, the heat in the upstairs gets to the point that the thermostats typically top out at 99 degrees (ouch). We got the new standing air condition units and they run such high amperage last season (yes, the energy star rated ones) that it cost us about $500 / month to run them only at night.

Mansard Roof: It has an extremely low pitch to it, it's 17-18 inches at the peak from the top of the rafters. There is blown in insulation in that part. there appears to be 1 vent, which looks like a straight metal pipe. I think it may be the house vent, though? For ovens and such? I am not sure. The sides of the Mansard roof come down to the top of the first floor and have no vents anywhere (even though I expected some)

I really want to make this house more efficient. It is costing us a lot of money every year and it has to be the way this roof was installed back in 1972.

Any clue? There seems to be some quality experts here, so I hope I hear some good news :)

My only thoughts were to install some sort of venting (I know nothing about this, just conjecture) and possible put vents in the soffit area to have cooler air to draw from.

Thanks in advance!!!

[Wgoodrich]

A mansford roof is really only a decoration. If built properly you could remove the mansford roof completely, install an exterior siding of your choise and it should not have changed the insulation blanket or cause the house to leak in a rain. It is only for decoration.

Now you should have straight walls on the outside of your rooms made of studs. These walls are supposed to have a vapor barrier on the inside surface of the studs then the drywall should have went over that plastic sheet serving as your vapor barrier. You then should have 3 1/2" of fiberglass insulation installed between the studs of those walls. If you opened up to get in between the exterior wall and the rafters of the mansford roof you should find nothing but an attic. This attic is nothing but an elaborate soffitt area.

Now there are some mansford roofs that land on top of the outside wall on the first floor without an overhang. This design requires you to pull up any plywood flooring in that mansford roof attic area and insulation should be installed between those joists that would be a part of the ceiling of the rooms downstairs needing insulated because the mansford roof area should be a cold air chase only that channels air from soffit vent at the bottom of the mansford roof into the attic and out the roof vents.

You should have styrofoam shutes keeping the air flow open above the outside walls between the top plate and the bottom of the roof decking. You should have enough roof vents installed close to your peak of your roof to meet minimum number per code rules. You should have enough insulation blown in the attic to meet minimum code rules also.

If I were you I would open up those mansford roof attics and see how it is insulated. Bet you don't find insulation below the mansford roof attic floor that is the ceiling for your lower floor ceiling. Just a guess

Wg

[andydiy]

Front House View:
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Soffit view
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Rubber Roof, 3 vents and a pipe for?
2476

Chimney and a pipe for?
2477


Now you should have straight walls on the outside of your rooms made of studs. These walls are supposed to have a vapor barrier on the inside surface of the studs then the drywall should have went over that plastic sheet serving as your vapor barrier. You then should have 3 1/2" of fiberglass insulation installed between the studs of those walls. If you opened up to get in between the exterior wall and the rafters of the mansford roof you should find nothing but an attic. This attic is nothing but an elaborate soffitt area.

That sounds like what I recall from some of the room renovations I have done over the years. I have never opened the Mansard roof which goes down the side of the house to the soffit, but I would expect it to be empty except for some blown insulation that may have dropped from increasing the insulation of the attic.

Now there are some mansford roofs that land on top of the outside wall on the first floor without an overhang. This design requires you to pull up any plywood flooring in that mansford roof attic area and insulation should be installed between those joists that would be a part of the ceiling of the rooms downstairs needing insulated because the mansford roof area should be a cold air chase only that channels air from soffit vent at the bottom of the mansford roof into the attic and out the roof vents.


There is no plywood flooring and the attic itself is not navigable except in the very center while sliding on a piece of plywood. The rafters are open to the cieling of the second floor (except for the insulation). Plus no soffit vents as shown in the picture.

You should have styrofoam shutes keeping the air flow open above the outside walls between the top plate and the bottom of the roof decking. You should have enough roof vents installed close to your peak of your roof to meet minimum number per code rules. You should have enough insulation blown in the attic to meet minimum code rules also.

I am not even sure how to check that since the height at the walls is about 1-2 inches in height :( I can't get anywhere near it.


If I were you I would open up those mansford roof attics and see how it is insulated. Bet you don't find insulation below the mansford roof attic floor that is the ceiling for your lower floor ceiling. Just a guess


Insulated as mentioned above.... insulation between the rafters above the second floor cieling. Possibly some falling into the walls, but I doubt a whole lot.



So - where to go from here? It seems like it 'may' be vented properly, but the vents look pretty shoddy and none are power vents.

The roof is seriously acting like an oven at this point :( It's 9:00pm and 98 degrees upstairs. It was only 87 today. Our room's air con has been running nonstop for the last 4 hours with the doors closed in that room and the temperature in there is 85. And it is a plenty big enough unit.

There has to be something wrong if the heating and cooling are costing us this much :) Would it be worth it to install soffit vents and then add a couple power vents (maybe the solar kind) to the roof?

Thanks again, I truly appreciate your thoughts on the matter.

[CR500]

WG has the description right when it comes to Mansards.

My house has a mansard roof and I hate the look and the poor insulation in my walls. One neighbor did rip off his roof, continued the bricks up in its place and installed a conventional roof. Too $$ for me but it looks and performs great.

Like you, I don't have any soffit vents. The insulation in my walls has billowed away from the studs into the mansard allowing large gaps for the air to sneak around. There is no opening between the mansard and upper roof. I do have four passive (mushroom) vents and one power vent that runs from 8am to 8pm. I loaded the upper roof with R41 insulation and it did help some. I recently installed a 94% furnace and it also helped some but without fixing the insulation in the walls and properly venting the upper attic there's not going to be much success.

[andydiy]

My house has a mansard roof and I hate the look and the poor insulation in my walls. One neighbor did rip off his roof, continued the bricks up in its place and installed a conventional roof. Too $$ for me but it looks and performs great.

Way too much $$$ for me too. I'm sure it would look awesome, but that would cost tons of money and my house would be super-tall :)


Like you, I don't have any soffit vents. The insulation in my walls has billowed away from the studs into the mansard allowing large gaps for the air to sneak around. There is no opening between the mansard and upper roof. I do have four passive (mushroom) vents and one power vent that runs from 8am to 8pm. I loaded the upper roof with R41 insulation and it did help some. I recently installed a 94% furnace and it also helped some but without fixing the insulation in the walls and properly venting the upper attic there's not going to be much success.


ok... so the insulation you are talking about is in the lower part of the Mansard roof - above the soffits and below the roofline? I haven't looked in there, but I suspect that it doesn't meet up with the upper attic like you suggest. I thought that it was said somewhere that putting insulation in there would lead to rot?

The venting - I have the 3 vents (are they ridge vents?) that look beat up. Maybe they aren't even working. I have NO power vent at all and would guess I need one.

The pipes, I can only guess, are venting for drains and such?

If I installed more venting, where would it be pulling the air from? I would definitely want to do this the right way. It is now 70 degrees (at 7:52 am) and 85 degrees upstairs. I can't imagine the temperature up there today when it hits 92 like it is supposed to :) It's cooking me. haha.

Thanks again guys!

[andydiy]

ok... being an engineer... I started thinking about this from an 'air flow' perspective.

Looking at the picture above... It looks like I have 3 ridge vents at the roof peak. Since there are no soffit vents and the soffit probably doesn't even meet up with the upper attic..... how can those ridge vents even remotely be doing anything? Where would the air flow come from (except maybe in the house) through the sides of the attic entryway door?

Seems to me that the air is 'stuck' in the attic and can't be released through the vents.

If I replaced the vents with larger dormer vents in to peak, where could I even get cooler air from? Since the roof is sooooooo shallow of a slope, where would it pull the air from? I assume that if I put smaller vents at the base of the roof, it would pull through them from outside? Would that help?


Still frustrated with this house.... is it possible that it will just spontaneously combust and I can let it burn to the ground :) haha

[Wgoodrich]

I learned a lot after looking at your pictures. Pictures do wonders in helping to understand conditions. First thing I notice is a prediction you are having leaky roof problems. Reason I say this is instead of normal shingles on the high roof part you have roll roofing. Roll roofing will not last near as long as regular shingles. If your high roof is at least 3/12 pitch I would refoof this area with normal shingles that should last 15 to 20 years if you have 25 year shingles in my experience. Then if you look close at your roof vents they are installed wrong. Look at the shape of the roof vent. The part that is solid and angled from the top of the vent to the roof line is supposed to be pointed up. Right now you have an angled roof running water down that roof line to that roof vent then the water is passing through the screen of the roof vent into your attic. Somewhere you have water damage in your attic from this constant leaking of rain water into the attic due to incorrect installation of the roof vents. Then it does not look like you have anough high roof vents. The minimum number of vents is 1 square foot of vent for 150 square foot of attic. Measure from the outside the width and the length of the attic. Multiply the width times the length and divide by 150. A vent is about one square foot. Then answer you come up with is the minimum amount of roof vents you need up on the high roof part.

Now take a piece of paper and sketch the square foot print of your house. Your mansford from what I can see ends with no soffit but right on the top of the exterior walls. Sketch the two floors of your house on the foot print you have drawn. Draw the angle of the mansford roof. then to high roof angle. Now at the top of the mansford draw a line depicting the framed wall inside your second floor. Look where it hits the ceiling of the first floor. The distance from that wall line where it hits the first floor ceiling measure out to the far side of the mansford is the area most often never gets insulated above the first floor ceiling. This would be a massive heat loss.

Now you can enter the mansfor attic in two manners. One just to look in and one to enter if you need to. You have your high outlet roof vents we discussed above. Now you need inlets from low on the mansford roof. All you need to do is climb up and cut a square hole through the mansford roof about a foot above the exterior wall. While that hole is open you can look in and confirm if the insulation is intact on the second floor walls and if insulation has been installed in the joists between that second floor and the mansford roof line that would be the ceiling for the first floor. This area must be insulated as heavy as your attic area. Once you have confirmed your inspection of inside the mansford attic area install roof vents like the ones up high over those holes cut through the mansford roof a foot above the exterior wall. Remember to properly install these vents so the sloped part is facing up to shed water and the screens are on the side and bottom. Work the vent under the shingles on the top of the vent and under the shingles on the side then on top of the shingles on the bottom of the vents. Install as many vent to allow air in that attic that you have number of vents installed up high on the roof now.

The attic area shutes I am talking about are about 4' long. You should be able to see them stapled to the bottom of the roof deck on top of the second floor walls creating a clear path of air from the mansford roof into the attic. If they are not there you can install them by shoving new styrofoam shutes along the bottom of the roof decking through where the wall meets the rafters and further so they will reach into the mansford area an inch or two. This will create your air flow without disturbing existing insulation in the upper attic.

If you must enter the mansford attic area most people will either cut a hole through the walls upstairs to enter the mansford attic area and when done reinstall the insulation and staple a piece of visquine over the hole then either install a false vent grill over the hole for future entry or simply patch the drywall and tape and bed and repaint.

I also suspect you should look at the pipes passing through your high roof area. There should be a rubber boot installed over that pipe and under the high part of the roof and over the low part of the roof around those pipes to ensure no water leaking around those pipes passing through the roof.

That should be a good start. Sounds like a lot but can be done in a day or so by the homeowner if so desired. You will make your money back in less than one year in energy savings and comfort.

Good Luck

Wg

[Wgoodrich]

Just to explain why the trouble of correcting your venting. If you have the proper amount of roof vents properly installed in the high part of your roof along the ridge and you install the intake roof vents low on the mansford roof and install those air shutes as discribed to ensure air flow from mansford attic to high attic the attic will cool 20 degrees or more in about an hour. Remember heat rises. If you allow cooler air in low and free air flow up to the high vents hot air will rush out the high exhaust vents without any power vents used. Also go in your crawl space and look to see if styrofoam insulation has been installed sealing the perimeter foundation walls. Then look to confirm you have plastic sheet covering your crawl space floor. Also look to see if you have vents in your crawl space equal to 1 square foot of vent for each 150 square foot of crawl. This will also save you energy and add comfort.

Just added thought

Wg

[andydiy]

Here is an approximation of how the house is laid out:

2482

Not a great drawing, I know :) But should get the point across. The dimensions show a VERY low pitch for the room, so I assume shingling would not work too well. I did not see any water damage, but with the tiny crawl space (18" max height at the peak) it was difficult to be sure.

House is approximately 26x40, which would require 7 vents according to your calculation.

Now take a piece of paper and sketch the square foot print of your house. Your mansford from what I can see ends with no soffit but right on the top of the exterior walls. Sketch the two floors of your house on the foot print you have drawn. Draw the angle of the mansford roof. then to high roof angle. Now at the top of the mansford draw a line depicting the framed wall inside your second floor. Look where it hits the ceiling of the first floor. The distance from that wall line where it hits the first floor ceiling measure out to the far side of the mansford is the area most often never gets insulated above the first floor ceiling. This would be a massive heat loss.

I think you mean the second story walls are not often insulated, correct? I don't recall if they are or not, so would have to dig into the walls to find out for sure.


All you need to do is climb up and cut a square hole through the mansford roof about a foot above the exterior wall. While that hole is open you can look in and confirm if the insulation is intact on the second floor walls and if insulation has been installed in the joists between that second floor and the mansford roof line that would be the ceiling for the first floor. This area must be insulated as heavy as your attic area. Once you have confirmed your inspection of inside the mansford attic area install roof vents like the ones up high over those holes cut through the mansford roof a foot above the exterior wall. Remember to properly install these vents so the sloped part is facing up to shed water and the screens are on the side and bottom. Work the vent under the shingles on the top of the vent and under the shingles on the side then on top of the shingles on the bottom of the vents. Install as many vent to allow air in that attic that you have number of vents installed up high on the roof now.

About a foot above the exterior wall of the secondfloor (where the mansard ends and up the slope), is where I should cut? I think you are saying to check the walls for proper insulation on the second floor, but I am getting confused :) Sorry.


The attic area shutes I am talking about are about 4' long. You should be able to see them stapled to the bottom of the roof deck on top of the second floor walls creating a clear path of air from the mansford roof into the attic. If they are not there you can install them by shoving new styrofoam shutes along the bottom of the roof decking through where the wall meets the rafters and further so they will reach into the mansford area an inch or two. This will create your air flow without disturbing existing insulation in the upper attic.

I don't believe there are any of these.. if there were, wouldn't there be associated soffit vents? Or am I missing what you are saying (very likely) :) It sounds like you want shoots that go through the full mansard (side of house part of roof) for the purpose of air flow, which means adding a soffit vent, I think.


Yes, there are rubber boots on both the pipes :) Yay, one thing seems correct!


Also go in your crawl space and look to see if styrofoam insulation has been installed sealing the perimeter foundation walls. Then look to confirm you have plastic sheet covering your crawl space floor. Also look to see if you have vents in your crawl space equal to 1 square foot of vent for each 150 square foot of crawl. This will also save you energy and add comfort.

It is possible that there is styrofoam insulation there, but hard to tell with the small crawlspace. I think I would have to open the roof to find out. There is no plastic sheet covering the crawl space floor (I assume crawl space means the high attic).


PS - I am going to add pictures of the attic to this post from another PC in a minute......

[andydiy]

Just a few attic pictures. The insulation is quite tall, so it is impossible to see where the end of the room meets the walls :(

2483

2484

2485

2486

[Wgoodrich]

I know it will not be fun but you can put a breathing mask on and swim through your blown in insulation and get close enough to shove the styrofoam shutes over your walls from the attic into the mansford roof attic area using a push rod with a flat tee on the rod to push the styrofoam shutes into place at least every third rafter space. This will open the air flow where it is requried to be. Right now your insulation has blocked off any air flow between high attic and mansford attic. Won't be fun but will do wonders in cooling that attic letting air into the attic from the mansford attic area to exhaust out your high vents by the ridge.

You missed where I am predicting no insulation. The floor of the second floor will extend beyond the wall of the room extending to the outside wall of the first floor. In your case this is about 2' wide from second floor wall to where first floor wall is. If you were in teh mansford attic you would be walking on this 2' area. This serves not only as the walk surface of the mansford attic area but also as the ceiling to the heated room below. This often is uninsulated and a high heat loss area. Insulation should be installed between these ceiling joists that are horizontally run from the second floor outside wall to the first floor outside wall.

When I said climb up and cut a 1' square hole I meant climb up a ladder on the outside and cut a 1' square hole through the mansford roof from the outside into the mansford attic. This hole should be cut and vents installed same as you have on the high roof only installed about a foot above the bottom of the mansford roof location right through the mansford roof itself. While this hole is open before you install the vent you can look in to confirm insulation is in the second floor wall lookng straight through that cut hole and in the first floor ceiling joist looking down from the cut hole to the horizontal ceiling joists being about 2' wide by my guess.

Once you install those vents through the lower part of the mansford roof into the mansford roof attic the air then can flow up to the top of the second floor wall through those shutes you need to install then through the high attic and exhaust out the high roof vents that you don't have enough of. The cool air entering the lower part of the mansford attic will move any hot air up [heat rises] through the shutes through the high attic and out the high vents allowing air flow that will cool both attic areas by 20 degrees or more. This will greatly reduce the work your a/c unit will have to do to cool that second floor cutting your energy bills and adding comfort to your home.

The styrofoam insulation in the crawl, I am referring to the area below the first floor unless you have a poured concrete floor. If you have wood floors on the first floor then you have a crawl space below that first floor that also is supposed to be insulated and vented and with a vapor barrier over or under the pea gravel down there.

Hope this helps

Wg

[andydiy]

ok, I get it. I am not sure how close I can get to the edge, though, since it tapers rather quickly. When I put rolled insulation in (a couple years before I had insulation blown in), I couldn't get anywhere near the edge because it tapered so quickly :(

Would it not be better to just put in soffit vents with the styrofoam shutes right above them? That way it wouldn't look as bad. I can imagine with vents on the side of the mansard would look a bit odd.

I see what you mean about insulation... you are saying the ceiling of the 1st floor (second floor flooring) is probably not insulated and the worst part of that would be the overhang at the base of the mansard, correct? So, this needs to be insulated. That would be the 6" space where the mansard overhangs and then meets up with the first floor cieling. I think I get that.
And the reason to create the vent above the floor level is so that you can insulate at the floor level (The wall should already be insulated). How am I doing?

We do have a poured and finished basement, BTW.

What would be the best way to insulate, then? Should I have insulation blows into the mansard portion below where the cutout would be (1 foot above the base of the mansard roof)? Or would I put the shutes in and blow insulation throughout the mansard and around the shutes?

[andydiy]

I think that I may have it all right in that last post :) My one question is... would it be possible to shingle the top with such a low grade/slope? I don't want to cause any unnecessary problems, but would prefer the roof to be as leak-proof as possible.

[Wgoodrich]

You install the shutes above the second floor wall between the under side of the roof deck and the top plate of the second floor wall to ensure air can flow between the two attics. Remember that mansford attic will get as hot as the high attic without proper ventilation to push the hot air out the high vents.

If you insulate the floor of the mansford attic you would be insulating over your living area of the first floor where it needs insulation.

Most basements require an R10 insulation minimum. To do this I would install 2" styrofoam over the basement walls. If you build false wood stud walls then keep the wall at least 2" away from the masonry wall so air can flow to dry up any wicked moisture of that masonry wall. Install friction style fiberglass batts same as any other stud wall is done.

Now there has been a couple of comments that the fiberglass insulation fell out of the back of these stud walls in both the basement and in the mansford attic area. To resolve that problem enter the attic and staple either 3 wood strips called screen stock or staple 3 webb strips across the back of the studs in that void area to hold the insulation in place within the stud walls.

If you look at the picture you provided it looks like you have about 36" from the roof deck to the top of the exterior wall. To find how much angle your roof has it is easy to carry a 12' long 2x4 and a 6' 2x4 on top of the roof. Set the one end of the 12' 2x4 on the ridge and set the short 2x4 like a leg to support the opposite end of that 12' long 2x4 from the lower part of the roof to the long 2x4. Use a level with a second guy and raise that 12' long 2x4 up or down until the level says that long 2x4 is level. Mark on the verticle leg 2x4 hits the bottom of the horzontal 2x4. Measure from the bottom end of that short 2x4 sitting on the lower part of the roof to where you made a mark on that 2x4. That distance will tell you the small number of your roof pitch. I am guessing by the picture it will be about 36". If that is true then you would have a 3' in 12' pitched roof. Shingles are allowed to be installed on any thing from 3' in 12' and more pitch roof. If you measure less than 36" on that 2x4 leg to your mark then you have less than a 3/12 pitch. In this case I would recommend a rubber roof installation installing a fiber board on the existing roof nailing it in place then glueing the rubber roof on that fiber board. This does two things. It greatly reduces the heating of the attic by that fiber board as insulation and allows at a later date if you need to strip that rubber roof by just pealing the surface off that fiber board underneath. I have rubber roofs on past 20 years and are now good as they were when they were installed. Roll roofing by my experience required me to replace them about every 3 to 5 years, Not fun.

Wg