Adding insulation to house exterior

[tthree]

House is a 1250 sq ft raised bungalow.  Built in 1963.  Cold climate: prairies of Canada.

We know the insulation is not great.  In the winter condensation runs down the walls from the screws in the drywall (worst on the SW side of the house).  Shockingly, the energy bill is not overly obscene.

As much as it pains me to remove the perfectly good wood siding from our home, I would like to add a layer of insulation and put Hardie board siding on the house.  This would most likely be a DIY job.  Does anyone have any advice/recommendations for adding insulation to the exterior of a home?

[zolotiyeruki]

Well, there are a couple of options that come immediately to mind:
Option 1) tear off old siding, glue on styrofoam panels, cover with normal sheathing, cover with house wrap, attach siding.  More expensive, but better vapor barrier and better sealed.
Option 2) tear off old siding, build new 2x4 or 2x6 walls against the outside of the walls, fill stud bays with batt insulation or blown-in cellulose, cover with sheathing and housewrap, attach siding
Both these options assume there's something on which the new thickness of the wall can rest.  Does your foundation stick out from under your walls?

What's the current state of the insulation in your exterior walls?  If you're going through all this trouble, it may be worth it to cut holes through the existing sheathing near the top of each existing stud bay and blow in insulation.

I'd be more concerned at this point about condensation and mold.  Do you have a vapor barrier?  If not, I wonder if it'd be worth it to strip all the sheathing, spray an inch of foam on the outside surface of the interior drywall, fill the cavities with insulation, and resheath.  If you're careful, you might even be able to re-use the sheathing.  And maybe even some of the shingles...

[Anomalous]

Posting to follow because I need to do the same thing to my house eventually, except that I need to replace all the windows as well (house built in 1961 with no insulation and single-pane aluminum-framed windows.)

I've read about a few different insulation techniques, but still don't know which is best.

If you want to go for maximum efficiency, you can look up the "chainsaw retrofit". This technique was invented in Canada. It involves lopping off all the overhanging parts of the roof, wrapping the walls and roof in a continuous unbroken layer of foam board insulation, and re-building the overhanging bits of the roof on top of the insulation layer so there's no thermal conduction path from inside to outside. Interesting technique to read about, but probably overkill.

[lthenderson]

I just did this exact thing a little over a year ago. We tore off the old siding, applied house wrap and resided with cement board. The housewrap did wonders for the insulation of the house. It cut down the drafts and reduced our heat bill significantly. Since our house was built in 73, the insulation was still in good shape so we didn't add the styrofoam layer between the sheathing and the housewrap for additional benefits.

[tthree]

Thank-you for all the responses.  We are still in the information gathering stage, so the more info the better.  It seems like around here the norm is to remove old siding, apply rigid foam insulation and re-side.  However, rigid foam insulation only has a R-value of 5.  So I am just weighing the options and considering cost vs efficiency.  We replaced the doors, windows and shingles 4 years ago, so ideally those would remain intact.

I will have a look behind the electrical outlets and see what is currently in the walls. 

[zolotiyeruki]

Thank-you for all the responses.  We are still in the information gathering stage, so the more info the better.  It seems like around here the norm is to remove old siding, apply rigid foam insulation and re-side.  However, rigid foam insulation only has a R-value of 5.  So I am just weighing the options and considering cost vs efficiency.  We replaced the doors, windows and shingles 4 years ago, so ideally those would remain intact.

I will have a look behind the electrical outlets and see what is currently in the walls.

The R-value all depends on the thickness of the foam.  R-5 in the pink XPS (extruded polystyrene) is a 1" thick board.  My local hardware store sells 2"-thick XPS panels, and you can always layer them if you want something even higher.

[Cromacster]

Whats the insulation situation in your attic?  Sealing and insulating your attic is going to be much higher bang for your buck over the insulation in the walls.  If you have a basement the next go to would be to ensure that the rim joist is sealed and insulated.  Then ensure the windows and doors are properly sealed and weatherstripped.  Only then, if you still find it necessary, do what you are thinking of doing.

Off the top of my head it's something like 15% of energy loss in a home is through the walls.  You can probably find the actual numbers with some googling.

[James]

Yes, the 1 inch foam doesn't add a huge amount of "R value", but it does some really important things. That R value extends over the conductive parts of the house, like the wood studs, so it breaks that conduction into the house. It also allows the placement of proper wrap which is huge. I doubt adding another inch on top of that would matter much at all for heating/cooling costs, and would add considerable issues with going around windows, etc with the siding.

So I would suggest simply adding the 1 inch foam, making sure everything is sealed perfectly both in the walls and attic, adding to attic insulation as needed, replace siding, and call it good.

[music lover]

The problem with the foam is that it is ridiculously expensive.

Have you considered pulling off the drywall and adding insulation from the inside? I did that when I replaced windows. It's cheap ($8 for a 4x8 sheet), but the mudding takes some skill. However, that also ensures that the vapour barrier is on the warm side of the insulation where it is supposed to be...foam on the outside can act as a vapour barrier which can lead to problems.

[zolotiyeruki]

The problem with the foam is that it is ridiculously expensive.

Have you considered pulling off the drywall and adding insulation from the inside? I did that when I replaced windows. It's cheap ($8 for a 4x8 sheet), but the mudding takes some skill. However, that also ensures that the vapour barrier is on the warm side of the insulation where it is supposed to be...foam on the outside can act as a vapour barrier which can lead to problems.

When I mentioned spray foam, it was in the context of spraying it on the inside-the-wall face of the existing drywall after removing the sheathing, so it would be in the same place a vapor barrier would be.  But yeah, a vapor barrier needs to be installed.

[cheapbarb]

A great source of information about all things insulation and energy efficiency is the build it solar website. Go to www.builditsolar.com and you will find a wealth of information about everything from frugal projects to state of the art passiv haus construction. Look into getting back copies of Fine Homebuilding from the library, as they have some articles about insulating and siding. When sourcing materials, look beyond the big box hardware stores to actual building supply companies. When I do this sort of work on my house I usually research materials through the manufacturer's website. Once I know what I want to use I contact the manufacturer and ask for a local dealer in their product.  It takes time, but it gives a better product and better results. Best of luck, and may you soon be sitting in your nice warm house watching the wind blow by outside.

[Goldielocks]

Thank-you for all the responses.  We are still in the information gathering stage, so the more info the better.  It seems like around here the norm is to remove old siding, apply rigid foam insulation and re-side.  However, rigid foam insulation only has a R-value of 5.  So I am just weighing the options and considering cost vs efficiency.  We replaced the doors, windows and shingles 4 years ago, so ideally those would remain intact.

I will have a look behind the electrical outlets and see what is currently in the walls.

What happens to the windows when you increase wall thickness?

+1 for vapour barrier being a huge increase in home efficiency for very little thickness.   if you like your siding, why not remove interior drywall, and add vapour barrier or thin layer of spray foam, then put up new drywall?  the drywall contractors are pretty fast, materials do not cost too much, just messy.  You can do it in winter, too.

[tthree]

Whats the insulation situation in your attic?  Sealing and insulating your attic is going to be much higher bang for your buck over the insulation in the walls.  If you have a basement the next go to would be to ensure that the rim joist is sealed and insulated.  Then ensure the windows and doors are properly sealed and weatherstripped.  Only then, if you still find it necessary, do what you are thinking of doing.

I was trying to keep the first post brief, but in doing so overlooked vital details.  When we bought the home 5 years ago we had a Energy Audit.  We did all the things recommended except insulate the exterior of the home.  The attic insulation was adequate, they did not recommend we add any.  The reason why we didn't insulate the exterior at the time, was the rebate was very small for doing this work but the project itself costs a lot.  You only would get reimbursed for a small % of the insulation, but the more costly part is re-doing the siding.  In the end we replaced the windows, doors, furnace, and insulated all the plug outlets/switches.  This work significant improved our energy rating.

Also when we bought the home 5 years ago the wood siding had just been painted.  Fast forward five years....and soon the exterior will need to be re-painted.  So now we NEED to invest some money into the exterior, so it make senses to invest money into the exterior and do the necessary insulation upgrades at the same time.

[tthree]

So I would suggest simply adding the 1 inch foam, making sure everything is sealed perfectly both in the walls and attic, adding to attic insulation as needed, replace siding, and call it good.

I like your thinking.  The more reading I do, the more I think this strategy is the most "bang for your buck".

[tthree]

When sourcing materials, look beyond the big box hardware stores to actual building supply companies. When I do this sort of work on my house I usually research materials through the manufacturer's website. Once I know what I want to use I contact the manufacturer and ask for a local dealer in their product.  It takes time, but it gives a better product and better results.

My BIL works at a local building supply company.  So we are able to get all the materials at below retail value.  He already has an opinion about what we should do, and I have an estimate of supply cost from him.  I posed the original question to see if the MMM community agreed with him or not:)  Sometimes he is cut corners kind of guy, so I want to make sure I weigh other options.

[tthree]

What happens to the windows when you increase wall thickness?

You can remove the old siding, add 1" rigid foam insulation, and reside without requiring any additional structural support. 

[tthree]

A great source of information about all things insulation and energy efficiency is the build it solar website. Go to www.builditsolar.com and you will find a wealth of information about everything from frugal projects to state of the art passiv haus construction.

Thanks for the recommendation!

[music lover]

What happens to the windows when you increase wall thickness?

You can remove the old siding, add 1" rigid foam insulation, and reside without requiring any additional structural support.

I believe they were referring to the change in thickness causing the outside window frame or brick mould to now be partially inside the exterior wall.

[Goldielocks]

What happens to the windows when you increase wall thickness?

You can remove the old siding, add 1" rigid foam insulation, and reside without requiring any additional structural support.

I meant, don't they get recessed by 1" or more? Is that a problem with the look or trim or flashing?

[tthree]

What happens to the windows when you increase wall thickness?

You can remove the old siding, add 1" rigid foam insulation, and reside without requiring any additional structural support.

I meant, don't they get recessed by 1" or more? Is that a problem with the look or trim or flashing?

Gotcha.  Currently our window and door trim sticks out further than the siding. So I don't anticipate adding an inch of thickness to the exterior will be an esthetic issue.

[James]

I meant, don't they get recessed by 1" or more? Is that a problem with the look or trim or flashing?

As long as the difference isn't too great, and the flashing is done properly, the siding can extent a bit past the windows and doors. I've seen this done, it works fine, but doesn't look as nice.

[cheapbarb]

I think that they make trim that brings the windows and doors out even with the siding.  Or you can replace the windows at the same time that you do the siding.  Also tthree, could you get a functional vapor barrier by painting the exterior walls (inside) with oil based paint or by putting up solid vinyl wallpaper on them? It's not perfect but it's a lot less expensive and messy than tearing apart the walls.

[wildfarm]

Hi tthree,

I think you're definitely on the right track with the exterior foam insulation. Prior to installing it, however, you might want to read up a bit on the proper thickness of foam for your specific climate. The folks at Green Building Advisor have a great tutorial at: http://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing. The issue is that in a cold climate such as you live in, if you add inadequate exterior foam you may actually cause moisture issues inside the wall, leading to potential mold and/or rotting issues.

The GBA article has a handy table detailing what your minimum exterior sheathing thickness should be...depending on whether your house is built with 2x4 walls or 2x6 walls, and where exactly you live, you'll require exterior sheathing between R7.5 and R15 to avoid potential structural damage issues. Regardless, 1" of exterior foam may just cause issues, since foam only has R value of 3.8-6.0 per inch, depending on the type you buy. 

Hope the advice is helpful. I'm definitely not an expert, just a guy getting ready to start construction on his own home in a few months who has spent a lot of time researching energy efficiency during the design phase. I'm continually amazed at how much building science has progressed over the past couple of decades.

Best of luck getting your house winterized!

[Jeremy E.]

I recently bought siding for my basement, I bought OSB boards and then put Fiber Cement Primed Cedarmill Strips on the OSB boards. The OSB boards are $10each and are 4'x8', the strips are $7each and are 8"x12', it ends up being just over $1/square foot if you do it yourself. Those strips will outlast me, so I shouldn't have to reside it ever again. Theres some cheaper options where you can buy weatherproofed wood siding for about $32 per 4'x8' sheet but they will only last about 15-20 years.

I'm thinking about building a house in the future, and I'm thinking I'll use Apex blocks, which are a foam/concrete form that gives an R35 R rating, and has lots of other good qualities like soundproof, fireproof, will outlast you, etc. Also you don't have to build forms which is a pain in the ... Butt. Another benefit maybe, very heavy so it will add thermal mass, although I'm not sure if the thermal mass needs to be inside the house to be beneficial.

[reader2580]

On an addition to my house in the 80s they used foam board as the sheathing.

[ncornilsen]

Reader, what else did they use for shear strength? diagonal boards?

[bacchi]

http://buildingscience.com/documents/insights/bsi-001-the-perfect-wall

Figure 9, at the bottom

"The best residential wall we know how to construct. Not cheap. Works almost everywhere – except in extreme cold climates where we would not insulate within the wood structural fame."

[reader2580]

Reader, what else did they use for shear strength? diagonal boards?

I have no idea.  When the crappy vinyl siding was removed from the addition I saw the foam insulation.  I never thought about what might be under the foam.

[paddedhat]

Reader, what else did they use for shear strength? diagonal boards?

I have no idea.  When the crappy vinyl siding was removed from the addition I saw the foam insulation.  I never thought about what might be under the foam.

Couple of options may be hidden under foam sheathing. One common technique is to use 1" foam, except for corners, where you use 1/2" OSB with 1/2" foam over. It all looks the same, from the outside, before siding. The other option is diagonal bracing. Old school was to notch everything to allow 1" x 4" wood bracing to be installed at a 45* angle, flush with the back of the sheathing. The modern version is a T-brace. A T shaped piece of steel that gets inserted into a single saw kerf. For these you just need to snap a chalk line then cut a shallow groove to tap the brace in. There are pre-punched holes to nail the brace to every stud.
As you might imagine, vinyl siding over foam sheathing is a pretty sad combo. Particularly since you can break into a house in a minute, by tearing the siding away, adjacent to the door knob. Next you punch a hole in the foam and take a hammer handle, or similar, to poke a hole in the drywall. Now it's as easy as reaching through the wall and unlocking he door.

[paddedhat]

I'm thinking about building a house in the future, and I'm thinking I'll use Apex blocks, which are a foam/concrete form that gives an R35 R rating, and has lots of other good qualities like soundproof, fireproof, will outlast you, etc. Also you don't have to build forms which is a pain in the ... Butt. Another benefit maybe, very heavy so it will add thermal mass, although I'm not sure if the thermal mass needs to be inside the house to be beneficial.

Think real hard before you take this leap. Like a lot of alternative techniques,  insulated block systems have strong proponents and nearly non-existent market share. The proponents tent to gloss over reality, including the fact that every step of the construction process, after the walls are up, tends to be more difficult, from structural issues, like attaching deck ledgers, and top plates for trusses, to mechanical and finish work. Siding and interior sheetrock can be particularly difficult and expensive. Next there is the issue that damaging insects simply LOVE foam. They love it like I love lobster and beer. Homes have been severely damages and even destroyed due to a toxic combination of termites and foam. They chew into it, build nests, and enter the interior unseen. Last, the actual process of pouring the concrete in the blocks can be a very difficult, tricky and lengthy process. At one point, when there was a bit of a blip in foam block construction in my area, some of the local concrete suppliers were refusing to do the work, since it tied up the trucks too long, and wasn't worth the hassle.

There are tons of options to build a home in non-traditional ways. The ALL have issues, some are ridiculous, and no intelligent builder would even bother. Other systems have obstacles that are outweighed by the benefits provided in the finished product. Knowing the difference is the hard part.

[RichMoose]

Wrapping the house in EPS or XPS foam seems to be the trend here, but it could actually make things worse. If you use foam on the outside and air seal it, you may get more moisture problems inside your walls. Most houses in AB were built with poly on the interior side of the studs (right behind your drywall). EPS or XPS foam is pretty much vapour impermeable, so the moisture has to be able to dry to the inside. With the poly, condensation with form in the wall cavity and your cavity insulation (most likely old fiberglass batts) will be wet. This will damage them decreasing their thermal performance, and may lead to mold and rot in your walls.

My recommendation would be to remove the wood siding, wrap the house in permeable building paper (Tyvek), then insulate with 1" to 1.5" Roxul boards. Attach your Hardieplank over the Roxul. You don't need strapping if your insulation is less than 1.5" thick. Roxul with allow the house to sweat to the outside, but moisture does not affect the insulation.

Good luck!

[tthree]

Wrapping the house in EPS or XPS foam seems to be the trend here, but it could actually make things worse. If you use foam on the outside and air seal it, you may get more moisture problems inside your walls. Most houses in AB were built with poly on the interior side of the studs (right behind your drywall). EPS or XPS foam is pretty much vapour impermeable, so the moisture has to be able to dry to the inside. With the poly, condensation with form in the wall cavity and your cavity insulation (most likely old fiberglass batts) will be wet. This will damage them decreasing their thermal performance, and may lead to mold and rot in your walls.

My recommendation would be to remove the wood siding, wrap the house in permeable building paper (Tyvek), then insulate with 1" to 1.5" Roxul boards. Attach your Hardieplank over the Roxul. You don't need strapping if your insulation is less than 1.5" thick. Roxul with allow the house to sweat to the outside, but moisture does not affect the insulation.

Good luck!

Thanks for the recommendation!  The Roxul boards sound like a superior alternative.  I have already downloaded (and started to read) the 91 page installation guide:)

[reader2580]

As you might imagine, vinyl siding over foam sheathing is a pretty sad combo. Particularly since you can break into a house in a minute, by tearing the siding away, adjacent to the door knob. Next you punch a hole in the foam and take a hammer handle, or similar, to poke a hole in the drywall. Now it's as easy as reaching through the wall and unlocking he door.

Really, what thief is going to take the time to pull back vinyl siding to see if there is foam insulation and then break through the foam and the drywall?  If they are that determined to get in then why wouldn't they just break a window?

My foam insulation is on a master bedroom addition so there no door to break in.  The vinyl siding has been replaced with Smartside.