Planning Your Home Addition

An addi­tion to your home can provide you with much needed space together with some fine craftsmanship and new functionality that may not have been available at the time your home was built.

Insulating Your Addition

Design-build house additions and room additions in Lincoln, Nebraska. Click here to go to this article.
Discover the most effective in­sul­a­tion for your old house.
An addition is a building project that adds living space to an existing structure. If the added space is alongside the existing structure it must have its own foundation. If we are adding up, for example, building a room over an existing garage, then the current foundation must be able to bear the added load of the addition.

Building an addition is very much like building a house, just smaller in scope. The same processes are required and work proceeds in very much the same order. In any organized urban area that has a building code, an addition will require a permit and occasionally a zoning change or exception.

But an addition has its own particular requirements. The big one is that the addition must blend well with the existing house. Sometimes that's a bit of a trick since the materials and techniques used to build the original structure are often very different from those used today.

Some Basic Rules for Planning Your Addition

The general process of planning an addition is the same as planning for any major renovation. But there are some major differences. The main difference is the perspective. In a typical renovation we are constrained to fit features and functions into an existing space. If we are remodeling your kitchen, for example, all of the cabinets, counters, appliances and other items required for a kitchen must be fitted into the space you have available in a manner that is both visually appealing and functional. The space constraint is the overriding theme of the design.

Planning for an addition typically very little space constraint. The space does not yet exist, which gives us some excellent opportunities. We can, for example, design the room to fit the kitchen, rather than forcing the kitchen to fit the room. Which leads to the first rule of designing additions:

Plan from the Inside Out

It is very common for some designers and homeowners to do the opposite: start planning with a certain size room on a piece of paper, then figuring out what will fit in the room, and how. Sometimes things are just squeezed into the room any way they can be made to fit. Doorways, hallways, closets, etc. can end up in strange places. This, obviously is not the way to do it.

Body Friendly Design: Design Ergonomics

Granite Countertop

We blend streamlined functionality with careful planning to adopt a kitchen to the needs and physical limits of its owners. Find out about ergonomic kitchen design and how the science of ergonomics helps to plan better kitchens here.

First the Function, then the Style

If you are blending an addition into your home, you want it to have the same overall style as the rest of the house, but avoid letting style dictate function. A common tendency, even among experienced designers, is to concentrate on the style elements first, and then try to fit the room's functions into the design framework dictated by the style. This is backward. Function first, then style.

In designing a kitchen addition, for example, a butler's pantry may be an entirely consistent style element for your 19th century home, but may not be the best functional dry-storage solution.

If you opt for the style rather than the function, you may end up with a lovely, but dysfunction kitchen — or at least a kitchen that is not as functional as it could be.

It's a lot easier to wrap style elements around a good functional design than it is to force function to fit around style elements. First the function, then the style is the approach that produces the best, most user-friendly, designs.

Be Flexible — The Rules are Made to be Broken

The third rule of designing additions is that the first two rules can and should be broken when appropriate.

Sometimes there are space limitations that do have to be dealt with — for example lot setback requirements that limit how wide an addition can be. And there just may be style elements that are on your "must have" list. If, for example, one of the motivating reasons for adding a kitchen wing is to find space to incorporate your grandmother's Hoosier baking station (complete with enameled table and zinc-plated flour bin), then that's what we will incorporate. There are better functional solutions to providing a baking station, but this is an instance in which style should override function.

New Building Technologies

The construction of an addition generally follows the same construction process as any major renovation.

There are some differences, however. One difference we like is that where in the typical remodeling situation we have to deal with walls, floors, roofs and other structures already built by someone else, when building an addition, we get to build our own walls, etc. so we know they will be square, plumb, level and structurally sound.

A second difference is the opportunity to use some new technologies that have vastly improved home building over the past 25 years.

The New and Improved Foundation

A ground-level addition needs a foundation to support its substantial weight, provide a flat and level surface for subsequent construction and isolate wood-based materials from ground contact. Wood in contact with the ground is prone to rotting and infestation by termites and other wood-loving bugs.

By far the most common material for foundations is concrete, whether in the form of poured concrete or concrete block. Others include brick and stone.

Conventional Foundations

Most additions rest on a raised, perimeter foundation that supports floors and load-bearing walls. There are two types: full perimeter and pier. A full perimeter foundation usually encloses either a basement or a crawl space or supports a slab. Pier foundations are almost always open structures — most suitable for storage buildings and vacation homes.

A block foundation is composed of 8" to 12" hollow concrete blocks bonded together with mortar and reinforced with rebar. This is a good, strong, foundation, generally less expensive but not as strong as poured concrete. Most of the cost of a poured concrete foundation is in the labor required to build the forms required to keep the wet concrete in place while it sets. In effect you are building two walls to get one: the forms, then the concrete wall inside the forms. When the concrete sets, more labor is required to remove and haul away the forms.

The choice of foundation is affected by personal preferences and costs. Basements can add thousands of dollars to the cost of an addition compared to the cost of a crawlspace or slab. However, when you consider the extra usable space created by a basement it is some of the least expensive space in a home.

Insulated Concrete Forms

The Jungle in the Dining Room

Solarium lantern
These homeowners created year-round summer in their dining room by adding a solarium, complete with tropical plants, a pond and a burbling waterfall. Click here to read the article.
The problem with basements in Nebraska is they are hard to insulate and tend to leak after a time — sometimes a very short time. Leak-proofing is a matter of effective waterproofing and drainage. Both have come a long way in just a few years — so there is no longer much excuse for a leaking basement in suitable soil.

The problem of effective insulation has been much harder to solve. The difficulty is that concrete transfers heat much too well. One solution is to attach foam insulation to the inside of the wall, another is to frame a false wall inside the basement wall and fill the false wall with fiberglass. This can be pretty expensive since essentially you are building two walls to get one. And, at best, you will end up with a whole wall insulation value of about R-7. Not very good, which is why most basements in Nebraska feel cold and damp in winter.

Technology has come to the rescue, however, in the form of Insulated Concrete Forms for foundation construction (actually, you can build the entire addition with them if you like). ICFs are concrete forms made of high-density polystyrene foam that are simply left in place once the poured concrete has set. They insulate the wall starting at R-17 and going up from there, and result in between 25% and 50% energy savings over conventional poured concrete basement walls. In the recent Oak Ridge National Laboratory tests of various insulated wall structures ICFs were the best performers. (Read the report here.)

The cost of ICF basements is about the same as that of a conventional poured concrete basement. The higher cost of the forms is offset by the savings in the labor required to erect the forms and by using less concrete — as much as 25% less with some ICF systems. But when compared to a concrete wall and applied insulation, the savings using ICF are substantial. As much as 20% over a conventional poured concrete basement. Combine this initial savings with the energy savings over the lifetime of the addition, and you are talking about one of the best construction bargains available today.

The New Science of Wall and Roof Framing

Once your foundation is in, we begin framing the walls and roof. There are a number of options for wall and roof building, from conventional stud framing to very "out there" approaches such as straw bale and rammed earth (we don't build any of these, by the way).

Conventional Framing

Since early in the 19th century, most residential construction framing has been stud or "stick framing". Stick framing replaced heavy timber framing (or post and beam construction) which had been the staple wood building system since the beginning of recorded history. It started in Fort Dearborn, Illinois, a town of fewer than 100 inhabitants. After the invention of stick framing by Augustine Taylor in 1833, most houses in town were built using this innovative, easier, system. At the time, local builders thought the notion of light framing was so ludicrous that they ridiculed it as "balloon framing," saying the buildings were so light they would just float away in a good breeze. They didn't. In fewer than 60 years the town had a million inhabitants and had been renamed Chicago.

Light wood framing is still a great structural system. Its only problems are that it takes a lot of wood and is so very hard to insulate. The most common insulation material is fiberglass batts inserted into stud cavities and stapled to adjoining studs and plates. So ubiquitous is this combination of framing/insulation that it is commonly referred to as "stick and batt".

Optimum Value Framing

Traditional stick framing over builds and wastes lumber resources. A strong movement to less wasteful framing has been building for two decades and has been adopted as a recommendation by the U. S. Department of Energy. Known as "Optimum Value Engineering", it is a collection of advanced framing techniques that eliminate many wasteful practices that have become standard over the years.

The effectiveness of stick framing has come into increasing question since the 1960s, and even the new OVE approach does not do much to allay these growing concerns.

• Lumber is continuing to increase in price and decrease in quality. Straight, high quality framing lumber is becoming scarce, and when available is getting very expensive. It has reached the point now that engineered lumber is becoming less expensive than traditional cut lumber, and is of much better quality. There is no likelihood that this situation is going to change for the better.

• Stick framed walls and roofs are very hard to effectively insulate (Read about it in Whole Wall Insulation). There are too many joints and gaps that permit air infiltration. Research has found that a space of as little as 1 millimeter inside a stud cavity is enough to start a convection current that transfers heat at an alarming rate. And insulation methods such as blown in or applied cellulose while more effective, are also considerably more expensive that the usual fiberglass batts.

• Conventional framed walls and roofs require a considerable amount of skilled labor and a lot of time to complete. Framing a house often takes two-three weeks during which time the entire structure is exposed to the elements. This exposure has been found to be a primary cause of mold infestation in new structures.

The solution to the problems of stick framing has been to abandon this 19th century technology and develop a whole new way of framing for the 21st century, most commonly called structural insulated panel framing.

Structural Insulated Panels

Structural Insulated Panels (SIPs) are prefabricated insulated structural panels used to frame walls, floors and roofs. They are made in a factory under controlled conditions and shipped to the job site, where they are joined together to construct the building.

A SIP is an engineered sandwich consisting a solid foam core 3.5 to 11.5 inches thick and structural facing (or sheathing on) each side. The facing is glued to the foam core under pressure. The foam in most products is similar to the Styrofoam in coffee cups. The most common facing materials are oriented strand board (OSB) and plywood, though manufacturers can customize the exterior and interior sheathing materials according to customer requirements.

They were first developed and tested by the Forest Products Laboratory of the United States Forest Service in 1935. Until about 15 years ago, they were not in wide use. However, the SIP manufacturing industry has greatly expanded in recent years in response to increasing demand by builders for labor, material, and energy saving products.

Speed of Construction:

The speed of construction using SIP framing is much faster. Walls and roofs can be erected quickly, saving time and money, without compromising quality.


Testing has shown that a wall panel with two, half-inch thick OSB skins many times stronger than a conventional 2" x 4" stud wall.

Thermal Insulation:

But, the greatest advantage of these panels is that they provide superior and more uniform insulation and a more airtight dwelling. This makes the building more comfortable, energy-efficient, and much quieter.

Recent tests conducted by the Oak Ridge National Laboratory (ORNL) found that SIP framing provides a much higher whole-wall R-value than a comparable stick framed house.

The study measured "whole wall" thermal transfer performance of SIP and conventional framed walls. Whole-wall measurements take into consideration heat loss due to seams and thermal bridging through wall studs, and are therefore more accurate than testing only the insulation material when measuring the R-values of buildings A 4-inch SIP wall scored R-14 on the whole wall tests, compared to R-9.8 for a 2" x 4" stud frame wall. The results of whole-wall tests of 6-inch SIPs compared to 2" x 6" wood stud walls were similar. The SIP wall scored R-21.6, while the wood stud wall scored a whole-wall R-value of 13.7. The most notable result was that a 4" SIP wall out-performed a 6" conventional wall.

These results are not that surprising, since SIP-built houses have fewer seams and therefore tend to be more airtight than stick-built houses. Also, since the insulation exists between two load-bearing panels, there is less framing needed in SIP building and therefore less thermal bridging through wall studs.

Comparative Cost:

The cost of Structurally Insulated Panels is usually reported in the trade journals as "more than" an equivalent stick built wall. That is not our experience. If you look only at the cost of the materials delivered. It's true, SIPs are costlier. But then the walls have to be built. A conventional wall has to be framed, sheathed (pronounced "sheeted"), insulated and dry walled. A SIP has to be erected — something like stacking Leggos®. A typical addition using SIPs can be framed in two days by two carpenters, compared to about 10 days for conventional framing. After the framed wall is up and sheathed, it still has to be insulated, then it has to be dry walled. That's two additional craftsmen, more time, and more money.

It's hard to know for sure without building two identical structures side by side, one with SIP framing and one with conventional framing, but our experience suggests that the overall cost of building with SIPs is about 20% less than building conventionally — which does not sound like much until you realize that $5,000 of framing will cost only $4,000 using SIPs. That is a savings equal to the cost of two or three very nice cabinets for the new kitchen.

The Construction Process

The construction begins at the completion of design. It is an actual process. It requires the "marshalling of the labor and material resources necessary to complete your project; ensuring any specialty trade contractors required are scheduled appropriately; inspecting and verifying that work was performed correctly, in compliance with building codes, and to generally accepted standards of workmanship; and that materials required arrive when they are needed.… more »

Need to learn more about designing, planning and building an addition? Try these articles:

  • Building by Design: The Design-Builder Concept
    A design-builder is a modern form of an ancient approach to building structures — that of the master builder. A master builder of old was a combination architect, engineer and builder, responsible for every phase of building a structure from initial concept to completion. Design-building firms such as StarCraft Custom Builders continue this oldest of building traditions.
  • The Construction Process
    Once your blueprints are completed, the real work begins. Your project manager works with you to develop a construction process that minimizes disruption to your household while work is in progress.
  • The Design & Planning Process
    If your plans include substantial changes to your kitchen or bath, or another room, or you are contemplating an addition; then a construction plan is required. Learn how your ideas are turned into a concept plan and then a construction blueprint in a three-step process using computer-assisted design.
  • Finding Some More Kitchen Space
    In many cases, existing kitchens are just too small for any real improvement in space management. Learn where to get more space, or at least the illusion of more space for your new kitchen.
  • Getting More Bathroom Space
    Our fondness of open spaces within the home doesn't end at the bathroom door. Unfortunately the acreage needed to create that spacious feeling just is not available in many older bathrooms. Often the key to updating a bath is creating more space — or at least the illusion of more space. This article examines where additional space can be found both outside and inside your existing bathroom.
  • Insulating Your Old Housenew
    Is your old house drafty in winter, swampy in summer? Almost impossible to heat and cool? That's because when your house was built a half-century or more ago, no one thought in­sul­a­tion was necessary — or, better said, experts believed that the 4" of dead air space inside the stud cavities of your walls was adequate in­sul­a­tion. Now we know better, and in an age of declining energy resources, adequate in­sul­a­tion in your old house has become a critical requirement. Learn how in­sul­a­tion works, and when and wear you should insulate your old house.
  • James Hoban: Master Builder (Sidebar)
    An Irishman designed and built the most famous house in American: The White House. Learn about this little known master builder.
  • Jungle in the Dining Room, The Solarium Addition
    These owners wanted to view a tropical forest through the French doors of their dining room. See how we built an indoor garden of tropical plants that doubled as a source of solar heating.
  • Living Through Remodeling: A Homeowner Survival Guide
    Remodeling will disrupt just about every routine you have; including some you are not aware of having. But this noisy, gritty process doesn't necessarily mean you will be tearing out your hair. With a little advance planning, it is possible to live through even major renovations with your sanity and good nature largely intact. Check out our remodeling survivors guide.
  • Your Old Windowsnew
    If the fine craftsmanship and charm of your old windows is quickly being eroded by cold drafts and frost on the panes, it may be time to consider doing something about them. Can your old windows be saved? If they are saved, can they be made as energy efficient as modern windows? The answer is "yes" and "yes". Most heritage windows can be restored and upgraded to rival the performance of a standard replacement window, and usually at a fraction of the cost.
Rev: 10/18/14