Your Home Addition: Planning Your New 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

Discover the most effective insulation for your old house, and why it is the most effective.

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 an 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 involves 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. This leads to the first rule of designing additions:

Body Friendly planning:
The Ergonomics of Design

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.

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.

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 dysfunctional 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.

Stay 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 steel countertop 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 in the typical remodeling situation we have to deal with walls, floors, roofs, and other structures already built by someone else while in 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 Foundations

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 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 these 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 several 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 uses more lumber than is strictly necessary and is hard to 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. Insulation methods such as blown-in or applied cellulose while more effective, are also considerably more expensive than the usual fiberglass batts.

Conventional framed walls and roofs also require a considerable amount of skilled labor and a lot of time to complete. Framing a house often takes two or 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.

A strong movement to less wasteful framing methods developed in the 1960s leading the U. S. Department of Housing and Urban Development to pioneer improved methods of stick framing known as "Optimum Value Engineering". These were adopted as a recommendation by the U. S. Department of Energy and are slowly trickling into building codes nationwide. There is nothing revolutionary about OVE. It is simply a refinement of conventional framing practices consisting of a collection of advanced framing techniques.

 Placing studs, rafters, and joists on 24" centers in place of conventional 16" on-center members.

 The vertical alignment of joists, studs, and rafters so they are exactly on top of one another. This ensures a straight and sturdy load path from roof to foundation through the strongest framing members.

 The elimination of double top plates. The second top plate or "bond beam" strengthens the wall and joins wall segments together. Aligning joists, however, makes strengthening the wall unnecessary, and steel strapping or splice plates do a better job of joining wall sections together.

 Replace jack studs to support window and door headers with steel header hangers.

 Omit headers in non-load-bearing walls, and make sure headers in bearing walls are sized to the span to be bridged and the load carried by the wall.

 Switch from conventional three-stud corners, which waste wood and are hard to insulate, to two-stud corners using drywall clips.

There are, however, some drawbacks to OVE framing. The first is that it does not save much wood or labor. Estimates by the U.S. Department of Energy put the savings at $250 for a 600 square foot addition. The labor savings is just 3-5% according to the Department of Energy in part because using a single top plate means that the framer cannot use pre-cut studs but has to cut his own. For this reason, even when using OVE techniques, many contractors still use a double top plate.

Secondly, some building codes have been slow to catch up with OVE framing, and many of the OVE methods are not approved by local codes, which leads to, at best, extensive negotiations with code officials.

Finally, although OVE can save costs on the construction end, these are often outweighed during planning by the need to design more precisely and in greater detail — processes that cost more money. For example, it is no longer enough to specify that a wall is a 2"x6" stud wall. With OVE it often has to be rendered in detail, showing the position, composition, and size of each framing member.

Structural Insulated Panels

Lumber is continuing to increase in price and decrease in quality, and there is no likelihood that this situation is going to change for the better.. 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.

Some contractors have switched to using Structural Insulated Panels, avoiding framing lumber altogether.

Structural Insulated Panels (SIPs) are prefabricated insulated 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 of 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 25 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.

SIP panels are somewhat more expensive per square foot than OvE framing but it is the better, and any additional expense for the product is saved on the labor side. Here is the breakdown:

The ORNL 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. True but only if just the cost of the materials delivered to the construction site is considered.

After delivery, however, the walls have to be built. A conventional wall has to be framed, sheathed (pronounced "sheeted"), and insulated. 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. That's two additional craftsmen, more time, 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.

Building Your New Addition

When our design for your addition is exactly the way you want it, and the working drawings are complete, we can begin building… (Continues)

Rev. 04/30/18