Specific home insulation question for the hive

Not mine, but I've been asked for ideas, and I don't have any (at least not any good ones), so here I am. The house in question is 1,000sq ft, single story stick-built, on a slab, about 50 years ago. The interior wall that carries the (very simple) plumbing and unsurprisingly faces the bathroom on one side and the kitchen on the other is noticeably hot on hot days. We're not talking about a hot spot; this is universally hot over the entire surface, when the weather is above 80F or so. I can only assume that the wall was not insulated and that the heat is dropping in from the poorly ventilated attic (another problem that needs to be addressed).

Without ripping off sheetrock and turning this into a major project, or hiring a company to spray in some sort of specialized foam or other loose material, is there a DIY-friendly solution to at least mitigate the problem? About the only thing I can come up with is to add a roll or two of fiberglass over the top of the wall in the attic, but that seems likely to be of limited benefit.

Is that the sunny aide?  If so, perhaps some nice shrubbery!

In reply to wvumtnbkr :

Nope, it's a totally interior wall. The exterior walls are sufficiently insulated that they are not a problem. The house has a shallow-angle shingle roof with gables on the north and south ends. The south side has a substantial hedge only about 10 feet from the house, and almost as high as the roof peak. There is little shade on the roof until late in the afternoon.

Is the house air conditioned?   Usually the top of an interior wall will have a continuous horizontal plate with only holes drilled for those pipes to pass through.   These days those openings get sealed after the pipes/wires are installed, not so much in the past.  Sounds like there is not enough insulation in the attic.   

The reason I asked if it was air conditioned.   Sometimes the return air part of the system will pull air into the house through all kinds of leaky openings.  I was wondering it it was pulling heat down out of the attic through holes in that wall,  Some older houses with whole house exhaust fans would do it if the windows were closed.  

I don't think the hot water pipes running through that wall could do what you are saying.

OBTW, I've never experienced such an occurence, and I didn't sleep in a Holiday Inn last night.

I've seen interior walls that didn't have a top plate. I'd get up in the attic and check the top of the wall first and add some boards or plywood strips to cap it. Some soffit vents and adding a continuous ridge vent would alleviate the hot attic issue.

The house has a couple of window units, no central air. Soffit vents and some sort of ventilation up high are definitely needed - I was thinking about one of the newfangled solar exhaust fans, but I've done no research to determine if this is a good idea or not. For the soffit vents, I'm figuring a 4" hole saw and a bunch of pop-in grills. I've never installed a ridge vent; the roof is relatively new, and I have no idea why they didn't install one at that time, but mine is not to question why. How difficult is a ridge vent to install?

The lack of a top plate sounds like the leading candidate here. I'll go up and check, but I've got a strong feeling I know what I'm going to find. The odd thing is that none of the other interior walls in the house exhibit this problem. How does one rectify this situation? Is it as simple as sticking some lumber in there to cap it off?

In reply to 02Pilot :

My house and garage got ridge vents when the shingles were replaced. I'm not sure what a roofer would do after it has been re-roofed. Maybe cut the top edges of the shingles after removing the cap shingles, cut out a few inches of sheathing on each side, insert the vent material and replace the cap shingles. I do know that my garage attic isn't the sauna it was before the vent was added.

I suspect the interior wall could be balloon framed (no top plate). Adding blocking to close off the stud cavities could help. Then maybe add some orange (fireproof) great stuff in any gaps to close off the wall cavity. 

Cutting in roof (or ridge) and soffit vents are pretty simple "handyman" tasks. Be sure to add insulation baffles between the rafters to allow uninterrupted airflow if new vents are added.

Alternately since the house is small and there are two gable walls - a louvered vent on each wall end might suffice for letting heat out. I wouldn't bother with a fan, just let physics do the job. 

In reply to OHSCrifle :

There are louvered vents on both gables - it is most assuredly not sufficient. I did consider trying to install a fan in one of them, again probably a solar unit so I don't have to mess with wiring.

In reply to 02Pilot :

How much insulation does the attic have?

In reply to OHSCrifle :

Good question. I'll pass by there tomorrow and check.

This thread brings up a question I've had in the past: How much do you want to cool off the attic? Is ambient temperature the goal? Is there a benefit to keeping it warmer in humid places like Florida?

You could add a simple attic fan wired to either a thermostat or humidistat to vent the area to ambient temp. Also a set of louvered dampers on the other side of the attic all wired together unless the soffits are vented. This is probably the least intrusive way to do it unless you think a solar powered fan would or could provide sufficient CFM to make any difference. All this could be done with a simple 20A 110V circuit.

I'd be willing to bet the kitchen has upper cabinets and a soffit over them. 
 

The soffit was framed before drywall, and the drywall came up to the soffit, then around it. That means the drywall is only 7' tall and the ceiling is 8'.  In the attic, this is a giant hole in the insulation 1' wide x 1' tall the entire length of the wall.

The heat of the attic fills that soffit box and the dumps down the wall.

Get in the attic and insulate the open soffit.  Before filling the soffit, caulk the holes around the pipes. 

I would add a mesh over the length of the wall in the attic then apply a layer of foam insulation over the mesh (mesh would be a support for the insulation) as an experiment

SV reX said:

I'd be willing to bet the kitchen has upper cabinets and a soffit over them. 
 

The soffit was framed before drywall, and the drywall came up to the soffit, then around it. That means the drywall is only 7' tall and the ceiling is 8'.  In the attic, this is a giant hole in the insulation 1' wide x 1' tall the entire length of the wall.

The heat of the attic fills that soffit box and the dumps down the wall.

Get in the attic and insulate the open soffit.  Before filling the soffit, caulk the holes around the pipes. 

We have a winner. I was just up there and found exactly what you describe. There's too much junk there for full access right now, but I was able to jam some insulation into two gaping holes around the dryer and toilet vents. At least now it's cut off from the heat in the attic by a layer of insulation. I'll go back in and finish the job once the attic is cleared out.

We found a solar gable-mount attic fan (40w, 1486CFM) that I will install to mitigate the heat build-up.

MrJoshua said:

This thread brings up a question I've had in the past: How much do you want to cool off the attic? Is ambient temperature the goal? Is there a benefit to keeping it warmer in humid places like Florida?

I'm reviving this because of this question.  I don't know the answer, but I am curious. 
 

I can't think of any reason you'd want the attic hotter. A delta of zero would just mean your AC would never turn on. 
 

Thoughts?

Maybe diminishing returns to actions to cool the attic past a certain point? Controlling the attic temp is means to the end of interior comfort and energy efficiency - so maybe there's a point at which doing something else is more effective than further action to bring attic temp to ambient. I have no particular expertise here, just spitballing

I really doubt ambient would ever be possible in any attic. It defies physics.

Heat will transfer from the warm side to the cool side. If there is more heat, there is more transfer. 
 

Assuming the attic is warmer than ambient, there will be more heat transfer (per square foot of exposed area) from the attic into the cooler living space than from the ambient exterior through the walls. 
 

Getting near ambient seems like a good goal regardless. 

Convection, conduction, and radiation are all happening simultaneously in a roof system.