Building Envelope Self-Help

Do you have questions about a building envelope problem you’re facing? Not sure where to go to find answers? We made this page for you.

Here you’ll find building science first principles, tips for better building, and a bunch of free resources you can use to research on your own.

last updated: September 17, 2024

Key Principles

There are a few key principles that can guide you to the answer of almost any building envelope question. Think of these principles as a an algorithm—a map—that will guide you to the right destination.

We’ve identified 9 key principles. Maybe there are more, and we’d be happy to update this list over time, but we think this is a good starting point. We’ll talk about each one in a bit of detail, but this is the overview.

1. It’s about water.
2. Gravity works—water flows downhill.
3. Water can also be carried by the air.
4. Keep the condensing surface warm.
5. Maintain continuity.
6. Match expected service life of adjacent materials.
7. Start with the code and manufacturer’s instructions.
8. Beyond code, think about risk.
9. Don’t make stuff up.

1. It’s about water.

The building envelope has a lot on its plate, from reducing energy use to aesthetics. The most important job of the building envelope, however, is to prevent water from getting to where it is not supposed to be.

It’s not that air leakage or aesthetics aren’t important. In fact, air leakage can play a big role in controlling water (we’ll come back to this). But when you have limited time, energy, money, and bandwidth you need to prioritize. And water is far and away the biggest enemy of your building.

It’s pretty rare that someone gets sued because a building is drafty or ugly. But people are getting sued all day long over water leakage that causes mold, rot, and corrosion. Mold, rot, and corrosion are big problems that cost big money to fix.

Keep water from getting where it is not supposed to be and your buildings will last longer and cost less to maintain.

2. Gravity works—water flows downhill.

It’s not hard to figure out how water will move; it goes downhill. Use this knowledge when designing and building.

There are two key concepts related to this idea that water moves downhill:

1. slope to drain
2. water-shedding laps

Let’s talk about each of these.

2.1 Provide slope to drain.

Slope to drain means that the surface water is flowing on is pitched, or sloped, towards a drain, roof edge, flashing edge, or other location where you want the water to go.

Makes sense, right? This cardinal rule of building envelope design, if followed religiously, would prevent many vexing problems.

It’s the low hanging fruit; just do it.

How much slope? Generally at least 1/4 inch per foot is a good rule of thumb, but the more the merrier.

The reason this is important is that slope to drain makes deficiencies in the water-control materials less likely to cause an actual problem.

A pinhole in the roof membrane probably won’t leak much if the water flows by quickly. But that same pinhole under a few inches of standing water will leak profusely.

2.2 Use water-shedding laps.

Another critical thing to keep in mind as you think about how water moves in and on your building, is that materials meant to keep water out should have water-shedding laps.

A lap is a transition between materials where one material is positioned over, or on top of, another.

When one material laps onto another, the higher one should lap over the lower one—like the shingles on a roof.

This seems obvious when talking about shingles (imagine how poorly the roof would work if you put them on backwards), yet materials like membrane underlayments are often installed in such a way as to “buck” water—the opposite of a water-shedding lap.

Even when materials are well-adhered or sealed, a lap that bucks water is more likely to deteriorate over time. It’s worse if it’s not well-adhered or sealed—water can go right in.

A properly shingled lap does not require any type of adhesive or sealant to shed water—it just works with gravity.

3. Water can also be carried by the air.

You’ve probably heard about air barriers. They’re used to—you guessed it—control airflow.

But, we bet you didn’t know that the main reason we care about controlling airflow is not about drafts, energy efficiency, or air quality (though those are all important). No, the main reason to control airflow is to control the movement of water!

The air can carry a lot of water. Mixed up with the oxygen, nitrogen, and other gasses in the air there can be a significant quantity of H2O, i.e. water in the gas (aka vapor) form. Water vapor is generally not a problem until it condenses somewhere and turns into liquid water. More on condensation in a minute.

The thing to remember is that airflow can carry moisture-laden air to a location where the water vapor condenses into liquid water on a moisture-sensitive surface and then we’ve got problems. Basically, airflow can bring water to where it’s not supposed to be.

To keep it simple, remember two things:

1. build airtight
2. keep moisture-laden air away from cold surfaces

4. Keep the condensing surface warm.

The condensing surface is where condensation forms. What’s condensation? Condensation is the process of converting water vapor (water in the gas form) into liquid water.

Condensation happens when water vapor encounters a surface that is below the dew point. Don’t worry about what the dew point is. Do remember that for any set of environmental conditions there is a magic number and when moist air touches a surface that is colder than that magic number, boom—condensation.

So, we just need to keep any potential condensing surfaces warmer than the magic number and we’re good! We can do this in a couple of ways:

1. insulate the potential condensing surface to keep it warmer
2. prevent the moist air from reaching the cold surface

This works in all climates, by the way.

5. Maintain continuity.

In the building envelope world it’s all about systems and assemblies rather than individual components. The best materials in the world are useless if they are not properly connected to one another to form a continuous assembly.

The vast majority of building envelope problems occur due to discontinuities in otherwise well-performing systems. It’s the connections between individual materials that make or break a system.

5.1 Think in terms of function not material.

It’s essential to name what a material does, not just what it’s commonly called.

Here’s an example: Self-adhered membrane (SAM) is a material that can serve multiple functions. SAM (the material) can be an air barrier (function), a vapor barrier (function), or a water-resistive barrier (function)—or all three.

The distinction is more than just semantics.

By referring to different components within our building envelope assemblies by their function rather than simply the material they happen to be, it helps both the designer and the builder. Referring to components by their function is a tool for thinking; it will point you in the right direction even if you don’t know the answer at the start.

There are four main functions that we typically talk about related to the building envelope. These four functions are to control:

1. liquid water intrusion (a.k.a. “bulk” water)
2. air flow
3. heat flow
4. water vapor diffusion

The four functions are listed in order of importance; controlling liquid water intrusion is the most important. Don’t worry about an item lower on the list until you’re got the ones above it nailed down.

5.2 Don’t lift the red pen.

Once you’ve got the concept of function rather than materials in mind, the next step is to maintain continuity of those functions throughout the entire building envelope.

The entire building envelope means “all six sides of the building” (the walls, roofs, and bottom level floors). Maintaining continuity means there are no breaks in the systems meant to perform each function (e.g. the system of components meant to control liquid water infiltration)**.

A good way to confirm that systems are continuous (or to identify any discontinuities) during the design process is to trace each system from one side of a detail drawing to the other.

Literally use a pen and trace. If you need to pick up your pen in order to get from one side to the other, then there is a discontinuity that needs to be addressed.

Repeat this process for every detail and every building envelope function (liquid water, air flow, heat flow, and diffusion).

You can also use the same process at a macro level to identify if you have enough details. Trace from one end of a wall section to another. If there is not a detail representing every condition that the pen traces over, it means there are missing details.

6. Match expected service life of adjacent materials.

Soldered copper pipes and garden hoses both transport water from one place to another. Both can be snaked through tight spaces, split into multiple branches, and terminated with various fittings.

It’s intuitively obvious that you wouldn’t want to plumb your house with garden hoses, though, because the hoses wouldn’t last as long as the other parts of your walls. You’d have to tear up perfectly good drywall to get access to repair or replace failed hoses.

We use soldered copper pipes for in-wall plumbing because the piping is intended to last the life of the structure. The same concept applies to building envelope components.

Wherever possible, match the service life expectations of adjacent materials.

This is especially important when materials are covered and will be inaccessible.

7. Start with the code and manufacturer’s instructions.

Always check the building code. For most situations the code will tell you how much insulation to use, where to put it, how to determine the roof wind uplift requirements, what performance criteria you need from your windows, and all kinds of other important stuff. Don’t skip code review.

Manufacturers’ installation instructions provide clear guidance on exactly how to use their products. The installation instructions will also tell you which accessory products you’ll need, and how to install those materials as well.

The code and manufacturer’s published materials are vast resources of information for better building that are often ignored. Don’t ignore them.

8. Beyond the code, think about risk.

The building code is more or less black and white. It says what it says and it’s the law to comply.

But when you get beyond the code the line between the “right” or “wrong” way to build something gets blurred.

So, it’s important to start thinking in terms of risk rather than right and wrong. Every choice should be a balance of risk against other factors like cost, schedule, and aesthetic preferences. The key is to properly characterize the factors and identify the decision maker so that person or group can make an informed choice.

9. Don’t make stuff up.

A lot of building envelope problems have occurred because good people took action with good intentions but without doing their research. In other words, they made stuff up.

Don’t make stuff up.

There is a wealth of information available to help inform building envelope design decisions. The second part of this page is devoted entirely to highlighting some of these resources.

Free Resources

Here in the 2020s, technical information about how to build good buildings is a commodity. It’s all freely available on the internet and anyone can find it.

Most firms like ours don’t have a secret vault of information that nobody else knows. We solve problems using the same freely-available information that we’re sharing below.

One last tip before we dive into the resources: it’s a great idea to explicitly reference some of these resources in your construction documents. Incorporating the resources by reference “buys” you a lot in terms of scope and detail with just one line of text. Since all of the resources we’re going to talk about are freely available online, contractors can access them as well.

We’ll aim to keep this list updated and add new resources as we come across them. If you know of a good resource you think we should include please chime in with a comment below.

Material Manufacturers

Material manufacturers all publish detailed drawings, specifications, and installation instructions for their products. Many also provide other design resources such as calculators.

After the building code, material manufacturers’ websites should be your first stop when researching a building envelope question. Always consult relevant material manufacturers’ websites for information during investigation and design.

U.S. Government

Various U. S. government departments and organizations publish building science and building envelope-related information online that is free to access and is a reliable source of good information. We’ll highlight a few.

Whole Building Design Guide

detailed guides, mostly commercial

The National Institute of Building Sciences (NIBS) under guidance from the past Federal Envelope Advisory Committee developed this comprehensive guide for exterior envelope design and construction for institutional / office buildings.

We love the Whole Building Design Guide. It’s full of straightforward advice and sound practices for a whole host of building envelope topics. There are sample details, links to relevant codes, standards, and additional resources.

Whole Building Design Guide

Building America Solutions Center

detailed guides, mostly residential

The Building America Solution Center provides access to expert information on hundreds of high-performance construction topics, including air sealing and insulation, HVAC components, windows, indoor air quality, and much more.

More focused on residential construction than the Whole Building Design Guide, the Building America Solutions Center has a wonderfully detailed library of guides that include background descriptions of topics as well as CAD details and beautifully illustrated retrofit strategies.

Building America Solutions Center

Cool Roof Calculator

Estimates Cooling and Heating Savings for Flat Roofs with Non-Black Surfaces

The cool roof calculator can be helpful when considering whether a solar-reflective roof will provide energy savings for your building as compared to a black roof. It’s very easy to use and results get better with more accurate inputs if you have them.

Cool Roof Calculator

Secretary of the Interior Standards

The purpose of the Secretary of the Interior’s Standards for the Treatment of Historic Properties…is to provide guidance to historic building owners and building managers, preservation consultants, architects, contractors, and project reviewers prior to beginning work.

If you’re working on any type of preservation project you should be referencing the Secretary of the Interior Standards. These guides clearly lay out sound practices for working with historic buildings. They’re easy to follow and break down various treatments into “recommended” and “not recommended” categories.

Secretary of the Interior Standards

Consultants

As it turns out many consultants like us seem to like to write about what we do and share what we know.

Building Science Corporation

One of the best sources that we’ve found for clear explanations of building science first principles are the resources published by Building Science Corporation.

BSC has published an extensive collection of white papers on their website covering most building science first principles topics in great detail. As a starting point, we’d suggest reading these 5 articles:

1. BSD-018: The Building Enclosure
2. BSI-001: The Perfect Wall
3. BSI-039: Five Things
4. BSD-013: Rain Control in Buildings
5. BSD-014: Air Flow Control in Buildings

CopelandBEC

Our own blog is a little more informal, though we hope you might find it entertaining and informative in bite-sized pieces that are easy to digest.

• conversational
• informal
• quick reads

We suggest you start here.

Industry Advocacy Organizations

Nearly every material, or type of materials, used for construction seems to have its own advocacy organization to promote its use. As part of their advocacy efforts these organizations publish a range of helpful technical content that is generally reliable and recognized within the industry.

Below are some examples, but this list is certainly not exhaustive. If you’re working with a material, chances are it has an advocacy organization—so do a web search.

Masonry

The Brick Industry Association (BIA)

Technical Notes on Brick Construction are FREE bulletins that contain design, detailing, and construction information based on the latest technical developments in brick masonry. Drawings, photographs, tables, and charts illustrate appropriate topics.

The Brick Industry Association (BIA)
BIA Tech Notes

Cast Stone Institute (CSI)

The Cast Stone Institute (CSI) was formed in 1927 by a group of visionary Cast Stone producers who identified the need to have a common voice for the Cast Stone industry. Today our mission remains, not only to be the authoritative spokesperson for Cast Stone, but also to provide expert counsel to the architectural and engineering communities.

Cast Stone Institute (CSI)
CSI Specifications
CSI Technical Bulletins
CSI Typical Details
CSI Technical Manual

Indiana Limestone Institute (ILI)

The Indiana Limestone Institute is a resource for architects, contractors, building owners and others seeking accurate, unbiased information about the use of Indiana Limestone in construction.

Indiana Limestone Institute (ILI)
ILI Handbook
ILI Technote Series

International Masonry Institute (IMI)

The Masonry Detailing Series (MDS) is an exhaustive collection of illustrative construction details and diagrams produced by International Masonry Institute (IMI) for architects and engineers to use as a design resource. This compilation includes hundreds of details for brick, block, and stone masonry systems, as well as details for ceramic tile, marble, terrazzo, plaster, rainscreen systems, terra cotta, AAC, and masonry restoration.

International Masonry Institute (IMI)
IMI Masonry Detailing Series

National Concrete Masonry Association (NCMA)

ICPI-NCMA unites, supports, and represents the producers and suppliers of concrete masonry systems – including concrete masonry, segmental concrete pavements, manufactured stone veneer, segmental retaining walls, and other hardscape systems.

National Concrete Masonry Association (NCMA)
NCMA TEK Notes
NCMA Manuals & Guides
NCMA Details

Roofing

Asphalt Roofing Manufacturers Association (ARMA)
Copper Development Association (CDA)
National Roofing Contractors Association (NRCA)
Single Ply Roofing Industry (SPRI)
Slate Roofing Contractors Association (SRCA)

Walls

Air Barrier Association of America (ABAA)
Wester Red Cedar Lumber Association (WRCLA)