InspectApedia Diagnose & Fix What's Wrong at Your Building (original) (raw)

Air and heat loss sealing points in buildings © Daniel FriedmanBuilding Insulation Placement

Index to key articles on where you should insulate

Index to Articles on building insulation installation:

Where to Place Insulation in Various buildings & Structures. This article lists articles describing how, where, and why to locate building insulation, house wrap, vapor barriers, and ventilation for different types of structures or different parts of a building. Is insulation better in the attic floor, or under the roof?

Where should we place insulation in an attic that has knee wall areas? How do I insulate a cape cod structure? The insulation detailing sketch for building air leak and heat loss problem points in buildings shown at page top is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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Building Insulation Placement - Where to Put the Insulation for Various Building Types & Structures

Foam insulation sprayed in a crawl space - this is not mold - Daniel Friedman 04-11-01 The insulation design and choice articles listed just below describe where to place insulation for various building types and situations.

This article series explains the insulating properties and relative costs of common building insulating materials including all types of building insulating materials such as fiberglass insulation, expanded polystyrene insulation, foil-faced polyisocyanurate insulation, and extruded polystyrene.

The insulation figure of merit, "cost of insulation per square foot R-value, is explained as a means of comparing insulating materials.

While the insulation cost data in the original article dates back to November 1983, the concept of using an R-value normalized cost to evaluate insulation is useful today.

Article Series Contents

Priority for Placement of Insulation

Reader Question: 13 Nov 2014 greg said:

I only have about half the inso I need to double the thickness in my attic. Which areas should I place this double layer?

Reply:

Greg,

If you do not have enough insulation to completely cover the attic floor with the thickness improvement you want, I would use one of the following approaches to choosing which locations in an attic floor are most-important to better-insulate:

  1. I'd put the additional insulation over bedrooms, allowing lowering of night time thermostat settings while keeping comfortable in sleeping areas
  2. I would put the added insulatin over those rooms below that form a single heating zone

The insulation detailing sketch for building air leak and heat loss problem points in buildings shown at page top is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss, and discussed

at ENERGY SAVINGS RETROFIT LEAK SEALING GUIDE.

Watch out: adding insulation over just part of a room or over just part of a heating zone is much like leaving a window open: the heat losses through the un-insulated or less-insulated areas, like air leaks in a building, can overwhelm the value of the additional insulation.

Question: insulating an adobe home in Arizona

2018/07/18 Sarah said:

I live in Southern AZ where is always dry and hot and we run our A/C unit from February through November. The home is built of single layer, 14’ X 7’ adobe blocks, and nothing else.

On some parts of the home the walls had been insulated and dry walled prior to our purchase.

We are adding a new bathroom in the garage, where there are simply the adobe block walls. The bathroom will utilize 3 new wood framed walls and the 4th wall will be along the original adobe block.

We wanted to leave the block as is so it would be a feature in the finished bathroom, but my husband decided to add framing to the wall to hide plumbing and electrical lines.

Now he would like to spray 2 part expanding foam insulation all over the wall to seal it and prevent moisture from coming IN through the brick when it rains.

I think that blocking moisture flow from one side will affect the brick as it won’t dry properly and may harbor mold. In addition, I am not keen on having foam insulation sprayed (by him) in the house as I have chemical-sensitivity-paranoias.

Since we are now covering that block wall with drywall after all is done, do we NEED insulation or water barrier behind it? It IS a bathroom, after all.

I was thinking of either not using insulation and applying a water barrier to the surface of the drywall OR using foam board between the framing he already installed, covering with drywall.

Do we need to apply a special water barrier/vapor barrier? Would it be better to allow air to flow freely through the blocks to dry things out? Thanks for your help! Have a great day!

Reply: use closed cell foam, skip the vapor barrier.

Bathrooms are a particular source of indoor moisture, even in usually-dry Arizona where a long hot steamy shower in a comparatively cooler bathroom can produce condensation on walls, floors, ceilings.

If the wall is insulated with any material that can absorb moisture, such as fiberglass or open-celled foam, then driving moisture into the wall can lead to trouble later with mold or even termites, even if the adobe blocks themselves don't care a whit.

In at least some Arizona jurisdictions such as Phoenix, a building code inspector will typically wantto see a water house wrap under exterior siding including synthetic stucco - that barrier is intended to let moisture escape out of the wall but keep actual water droplets from entering the wall from outside - e.g. from wind-driven (perhaps increasingly-rare) rain.

Vapor barriers are required on all projects unless waived by the Facilities Review Committee. ... Minimum 10 mil plastic vapor barrier is recommended under all slabs on grade. - CITY OF PHOENIX BUILDING STANDARDS AND REVIEW PROCESS Facilities Review Committee January 1997 Updated September 1998, April 1999, December 2000, November 2001, Effective July 1, 2006 https://www.phoenix.gov/streetssite/Documents/eas\_pdf\_building\_standards\_2.pdf 2018/07/19

If the interior is being sprayed with open-celled foam - that can take up water and trap it in the wall - it would make sense to include a moisture barrier (like 6 mil poly, not a house wrap that does not block moisture) on the interior wall surface before its finished surface of drywall is to be installed.

Some experts have pointed out that moist moisture moves into wall cavities at penetrations, such as around lights and wall receptacles or pipe and wiring passages, not through drywall itself - and they're right. So there's a defensible argument for skipping the vapor barrier on the wall interior side. But in any event if those penetrations are not sealed, even a poly moisture barrier will not do the job.

Bottom line opinion:

If this were my project I would insulate with closed cell foam - a water-proof material that, properly-installed, eliminates the issues. If hubby is using an open-celled foam take care to seal the wall penetrations.

Research, Codes, Standards on Insulation Placement in Buildings & on Mechanical Systems

...

Continue reading at BLOWN-IN INSULATION or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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INSULATION LOCATION - WHERE TO PUT IT at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING INSULATION

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Citations & References

In addition to any citations in the article above, a full list is available on request.