CONSTRUCTION SPECIFICATIONS

IN THIS ARTICLE
How Much to Specify
Types of Specifications
Good and Poor Examples
Where to Get Specs                           View all PLANS & SPECS articles

If construction drawings focus on a building’s shape, appearance, and dimensions, the written specifications, or specs, focus on what materials will be used and how they should be installed. What information goes in notes on the drawings, and what goes in the specs is up to the designer, but a good set of detailed specs goes far beyond what could possibly be put into a drawing. It’s OK if the same information appears in both places, but if there is a contradiction, the specs generally take priority, at least legally.

At a minimum, specifications list what materials to use,  and call out any special installation requirements. Specs are much more valuable if they go farther and provide detailed installation requirements and establish quality standards for the materials and the workmanship. Equally important is providing a measurable way to determine whether the work has met the standard.

On a large job, the specs will be broken down by trades, so there will be specs for the painting, roofing, concrete work, flooring, and so on.

On a small remodeling job, the roofing specs might be as simple as:

Existing asphalt roof shingles shall be removed and disposed of by contractor. New shingles shall be 25-year architectural shingles with 36-inch-wide Grace Ice-and-Water Shield, or equivalent, at eaves. Underlayment shall be 15-pound tar paper. Aluminum drip edge to be installed at eaves and along gable ends, and an approved aluminum vent at ridge.

On a high-end new home designed by an architect, the roofing specs might go a lot farther – stating  that the roof shingles must meet specific standards (UL) for fire resistance and (ASTM) for wind resistance, that the  “tar paper” underlayment meet a specific ASTM standard, and that the drip edge must be of a certain minimum thickness of aluminum. It may go further to state that the shingles must be installed within a certain temperature range, which may be more restrictive than the manufacturer’s requirements. For example:

Existing asphalt roof shingles shall be removed and disposed of by contractor. Site shall be left free of nails and other debris. New shingles shall be GAF Timberline Series 30 year architectural shingle, or equivalent acceptable to owner, installed as per the written manufacturer’s instructions, and within the temperature range recommended by manufacturer. All eaves shall be lined with 36 in. Grace Ice and Water Shield. Grace Ice and Water Shield shall also line all valleys and any roof areas with a slope of 3:12 or less. Underlayment shall be  ASTM D226 Type I or II asphalt-impregnated underlayment or an approved synthetic underlayment, lapped min. 6 in. at horizontal seams and min. 4 in. at vertical seams. Nails shall be double hot-dipped galvanized roofing nails of sufficient length to fully penetrate roof sheathing. Use step flashing at all roof penetrations; Flashing shall be .032 in. aluminum or 16 oz. copper or lead-coated copper. Use .032 in. aluminum drip edge at all eaves and gable ends. Install Air Vent Shingle Vent II at ridge, as per manufacturer’s written instructions.

HOW MUCH TO SPECIFY
Many construction jobs are done with no or minimal written specifications. The customer doesn’t really know what he or she is getting, and often is often disappointed with the results. In the absence of a written spec, you will often get so-called “builder’s grade” products, a euphemism for cheap and basic. Builder’s-grade windows are typically solid vinyl with very cheap screens that are difficult or impossible to remove without breaking them – I know, as I have some in my current home and previous home. Builder’s-grade doors, floor coverings, tubs, showers, bathroom fixtures, and cabinets share the same minimal price and quality.

If you want better, and if you want to know ahead of time what you are getting from a contractor, you need at least  basic written specifications, identifying the products that will be used, how many coats of paint or floor finish you are getting, and so on. Otherwise, it’s a complete crap shoot. If you are working with a quality-minded, conscientious contractor, you may get an excellent job, but why leave it up to chance?

You can’t and don’t want to spec every nail. But reasonably detailed specs will reduce your risk of getting substandard materials or workmanship, and it will reduce the risks of disputes over the completed work quality since the standards for material type, quality, and workmanship are spelled out in black and white.

How detailed a spec should be depends on the complexity and requirements of the job. I’d recommend basic specs, such as listing the product by brand and model, for just about every product and material to be used on the job. For paints and coatings, you will want to know what prep work will be done and how many coats of what paint will be used. Beyond that, you’ll want detailed specs for portions of the job that are very costly (or costly to fix, such as the foundation), critical to the success of the project,  prone to problems (like radiant floors), or require specialized products or workmanship that may be unfamiliar to the tradespeople doing the job. If problems show up after the work is done, you will be in much stronger position to get the work repaired if you have a written spec to fall back on. Examples of products or systems that should have detailed installation specs, and issues to cover in the specs, include:

  • Foundations – Concrete mix, strength, reinforcing
  • Concrete slabs – Concrete mix, strength, reinforcement, flatness, finish, expansion/movement joints, allowable cracks
  • Roofing – Type, weight/thickness/warranty period of roofing; type of underlayment, flashing, and fasteners. Carefully spec details for low-slope roofs, and for complex roofs with hips and valleys, detailing how valleys will be waterproofed. Get detailed material and installation specs for roofing materials such as wood, metal, tile, slate, and composite materials.
  • Windows and doors – Specify type, model, and energy efficiency. Also provide flashing details around doors and windows to prevent leaks, which are common here.
  • Skylights – Prone to leaking. Make sure installation follows manufacturers specs. Extra membrane flashing around skylights recommended in freezing climates.
  • Insulation and air sealing – If you care about energy performance, you’ll need to spec this carefully.
  • HVAC systems – A lot can go wrong here. System can be oversized, undersized, uneven, noisy, leaky (ductwork), and inefficient due to installation errors. See performance specs. 
  • Radiant heating – Needs careful specifications by an experienced designer or installer.
  • Wood flooring  – Moisture content, substrate, fasteners, vapor barriers (over slab), finishes. Follow the recommendations of the National Wood Flooring Association (NWFA).
  • Ceramic tile – Follow the methods and standards in the TCNA Handbook if you want trouble-free installations. Floor must be stiff enough. Also pay attention to substrates, adhesives, and movement joints.
  • Special construction for wind or seismic loads: This includes wind-resistant roofing, impact-resistant windows, engineered framing fasteners, and shear wall requirements.
  • Metal components in coastal areas: Make sure that any exposed metal flashing, fasteners, or hardware is stainless steel, copper, brass, lead, or double hot-dipped galvanized. Other metals and finishes will not last long due to the corrosive power of salt spray.

Over the years, I’ve learned to assume nothing about a job where the scope of work is not in writing. If the work description or construction drawing is not specific, you won’t really know what you’re getting until the job is done. You may be happy with it – or not, but changing it mid-job or after completion is always expensive and who will pay for the changes will always be contested.

If you know what you want, specify it. Do you want the nail holes filled with a color-matched putty on your natural woodwork – if so, put it in the contract. Otherwise you might find yourself filling several hundred holes by yourself after the job is “done.”

While you can’t spec every last nail, there are times when you have to spec things as small as nails. For example, I once built a gambrel roof using site-built trusses fabricated with plywood gussets. The nails in the gussets had to be a specific size, length, and number, and installed in a specific pattern for the engineered design to work. Using the proper type and size of nails and fasteners is also critical in truss hangers and other engineered framing connectors, as well as with tile backerboards, drywall (to prevent nail pops), and many other building materials.  So, in many cases, it does make sense to specify the nails.

TYPES OF CONSTRUCTION SPECIFICATIONS
Specifications may cover the properties and installation of products and materials, and systems. They are either written as product specifications, installation specification, or performance specifications. Quality standards are often a part of installation specs.

Product specifications. These can name specify a specific brand-name product, such as: “Foundation insulation shall be 2-inch tongue-and-groove Dow Styrofoam, or equivalent.” To give the contractor more flexibility it may provide a technical spec, such as  “Rigid foam insulation to be 2-inch-thick extruded polystyrene with tongue-and-groove edges, with a minimum compressive strength of 25 psi.”

The first type of spec, that names the product is certainly the simplest – no question about what is to be used. Language such as “or equivalent” or “or similar” are OK as long as you state in your contract that any such substitutions must be “approved by owner or owner’s representative.” In some cases, like with extruded foam insulation above, all major brands are pretty much the same. With other types of products, such as  paint, doors and windows, siding products, and composite wood products, equivalency is harder to determine. You’re better off finding the product you like and speccing just that.

Highly technical specs are probably overkill for most residential products, except in high-end jobs, and in instances where the design or code calls for specialty products. For example, if you are putting Styrofoam insulation under a slab or foundation, you will need a higher compressive strength than what is typically found in the lumberyard. If you are in an area where the code requires impact resistant windows, wind-resistant roofing, or special structural connections to protect against earthquakes or high winds, then technical specifications are essential.

Installation specifications. Most contractors and tradespersons have their own way of doing things. In the building trades, you’ll often hear things like “This is how I’ve always done it” and “I’ve always done it this way and haven’t had any problems.” That’s exactly what the contractor told me who installed a Velux skylight in a shallow roof, violating the manufacturer’s specs, and guess what – it leaked until I removed it and reinstalled it per the manufacturer’s instructions.

Unfortunately “the way we’ve always done it” may not work anymore due to changes in materials, codes, energy standards, or other factors particular to your job. The goal of installation specs is to avoid these kinds of problems. These describe, in detail, how a product is to be installed or applied. For example,

Install 2-inch Styrofoam extruded polystyrene insulation over interior side of basement wall by attaching wood furring strips vertically over the foam insulation at 16-in. or 24-in. on center. Fasten 1×2-in. or 2×4-in. furring strips through the foam insulation and into basement wall using Tapcon or similar screws that penetrate about 1-1/4″ into the concrete wall. Use 4 screws per 8 ft. furring strip.

Quality standards. Installation specs for visible finish work often contain quality standards as well (see also construction-quality contract language). Quality standards are only useful if they provide an objective, measurable way to determine if the standard has been met. For example, a Level 4 drywall finish, from US Gypsum, based on the standards of the Gypsum Association is as follows:

All joints and interior angles shall have tape embedded in joint compound and shall be immediately wiped with a joint knife or trowel, leaving a thin coating of joint compound over all joints and interior angles. In addition, two separate coats of joint compound shall be applied over all flat joints and one separate coat of joint compound applied over interior angles. Fastener heads and accessories shall be covered with three separate coats of joint compound. All joint compounds shall be smooth and free of tool marks and ridges. The prepared surface shall be covered with a drywall primer like Sheetrock first coat prior to the application of the final decoration.

While this goes into great detail about the installation, the only standard about the quality of the visible finish is that the joint compound should be “smooth and free of tool marks and ridges.” How smooth and free of tool marks is pretty vague.

A better quality standard is provided by the National Association of Homebuilders (NAHB) in their book of Residential Construction Performance Guidelines. This provides both performance guidelines and corrective actions. For drywall finish to meet their standard it must not have any of the following:

  • Any joints visible from a standing position, facing the surface at a distance of 6 feet under normal lighting conditions
  • Any nail pop, blister, or other blemishes that are visible from a standing position facing the surface at a distance of 6 feet under normal light conditions
  • Any drywall cracks greater than 1/16 inch in width
  • Any defects resulting in cracked corner bead, trowel marks, excess joint compound, or blisters in tape

This seems like a reasonable standard, although I’d apply the same standard to cracks as to other defects: Any drywall crack visible from 6 feet under normal conditions should be fixed.

Performance specs. This type of spec describes the standards that must be met, rather than the specific product of system to be used. The contractor will propose a product or system, which must then be approved by the owner or owner’s representative, such as an architect or construction manager.

Performance specs are often used for heating, air conditioning, and other mechanical systems. They may also be used for wells, septic systems, or other building components where the performance is more important than the specific products and materials used. In general, this is a practical and economical approach that puts the responsibility on the subcontractor or vendor to design the system. They have the expertise to do this efficiently and are accustomed to putting out proposals. They may offer some suggestions that differ from your specs, which are generally worth listening to.

A performance spec for an air-source heat pump might read:

Air-source heat pump shall cool all rooms in the house to 76°F degrees in summer with outdoor temperatures of 93°F, and heat all rooms in winter to 70°F with outdoor temperature of 25°F. First and second floor shall have separate heating and cooling zones. All ductwork to be galvanized sheet metal or insulated duct board, fabricated, sized, and installed in accordance with applicable ASHRAE and SMACNA standards. All ductwork joints shall be sealed with duct mastic (and fiberglass tape on ductboard). All ductwork in unconditioned spaces shall be insulated.  Heat pump to be Energy Star certified.

Special conditions. This type of specification would cover an special measures required on the job due to poor weather (too hot or too cold), difficult access, very steep or wet sites, environmental concerns, etc.

Special words and phrases. Certain phrases are commonly used in specs. Some are good, some not so good. The main ones to watch for are:

  • Workmanlike manner. It never hurts to specify that work be done in a workmanlike manner, but the definition is pretty fuzzy. See the legal definition of “workmanlike..
  • Manufacturer’s written instructions. Always include in you specs, where relevant, that all materials and products will be installed in accordance with manufacturer’s written instructions. Most manufacturers provide detailed installation instructions, which tend to be strict as they do not want to see product failures. If your contractor does not follow these instructions, any product warranties may be voided.
  • Match existing. This is commonly used in remodeling work. It’s best to find the matching product before you start. If your contract requires the contractor to “match existing,” make sure it contains a reasonable way to determine if it meets the standard, preferably that the match must be “approved by owner or owner’s representative.” (Read  about match existing in contracts.)
  • In accordance with all applicable codes. It doesn’t hurt to include this language and it might come in handy on occasion. For example, if the building, plumbing, or electrical inspector rejects a portion of the work for whatever reason, and the contractor claims that it will be an “extra” to bring the work up to code, you have a leg to stand on here. Building inspectors have a fair amount of discretion in how they interpret the code, so surprises like this do occur.
  • Or equivalent. Or phrases such as “or equal” or “or similar” often wind up in specs. This is fine as long as the substitution is “approved by owner or owner’s representative.” Once piece of drywall or fiberglass insulation may be as good as another, but the same is not true for most building products.

CONSTRUCTION SPEC EXAMPLES

Specifications do not need to be pages long, but they should call out the important details of the material and its installation. A well-written specification is good for both the owner and the contractor as each knows what to expect, leading to fewer surprises and misunderstandings.

Poor: “Composite-type decking, Trex or equivalent, fastened with hidden fasteners.”

Good: “Decking to be 1-inch Trex composite decking,  with square edge, installed with the Trex Hideaway Hidden Fastener System, in accordance with the manufacturer’s written instructions. Color to be selected by owner”

Poor: All exterior trim to be primed and painted with Benjamin Moore latex paint, or equivalent.

Good: Before painting, exterior trim to have exposed knots sealed with shellac or equivalent sealer. Exposed corners to be lightly sanded. All trim shall be primed on all six sides with Benjamin Moore Latex Primer 169, and receive two top coats of  Benjamin Moore Exterior Acrylic Latex Semi-Gloss K588.

Poor: Ceramic wall tile be installed over tile backerboard with thinset mortar. Grout shall be installed with movement joints, as needed, and sealed upon completion

Good: Ceramic wall tile to be installed with latex-modified thinset mortar over 1/2-inch Hardibacker fastened to wood framing with corrosion-resistant screws, in accordance with the backerboard manufacturer’s written instructions. All Hardibacker edges to be backed by solid framing. Grout color to be approved by owner. Grout shall be polymer-modified and sealed with Aqua Mix Sealer’s Choice Gold, from Custom Building Products. At all corners, tub edges, and changes of material, tile joints shall be grout-free and sealed with a resilient caulk to match the adjoining grout. All work shall be done in a workmanlike manner.

WHERE TO GET SPECS
If you are working with an architect, he or she will provide specs as part of the design process. Most architects use a system called Master Spec, a comprehensive specification system developed in conjunction with the AIA (American Institute of Architects). Master Spec is overkill for most small jobs – e.g., the short-form spec for residential wood flooring is 7 pages long – but it certainly covers all the bases and can be edited as needed (see Master Spec sample).

If the designer does not provide specs, they generally come from the contractor as part of his proposal and are often very minimal. For example: “Install architectural shingles over roofing felt as per plan.”

If you are writing your own specs, you should start by identifying as many products as you can by brand name and model. Perhaps you want Marvin double-glazed windows with argon and Benjamin Moore paints. For many of these products you can specify that they be installed “according the manufacturer’s printed instructions.” It’s better if you take a look at these instructions and include in the specs the most important details.

Most mainstream building products have detailed instructions from the manufacturer. For generic products, such as ceramic tile, you will find extensive product and installation specs published by trade associations for the industry (see list of trade associations).

Construction industry standards.  Trade organizations publish extensive standards for installing plywood, hardwood flooring, ceramic tile, wood shingles, and similar generic products that may not have instructions from the individual manufacturer. A stronger approach than just referencing “industry standards” is to cite a specific industry specification. For example: “Ceramic tile and backerboard to be installed according to the 2010 TCNA Handbook for Ceramic Tile Installation. Even better is to specify a specific standard such as “Install ceramic tile according to TCNA Standard RH110-10: For Radiant Heat on Concrete: Hydronic System.” These standards go into great detail about the preparation, materials, site conditions, and installation techniques required for a professional job.

They may also cite specific quality levels. For example, the Gypsum Association (GA), in conjunction with three other trade associations publishes detailed specs for installing gypsumboard. If you specify a Level 4 Gypsumboard finish, then “All joints and interior angles shall have tape embedded in joint compound and two separate coats of joint compound applied over all flat joints and one separate coat of joint compound applied over interior angles. Fastener heads and accessories shall be covered with three separate coats of joint compound. All joint compound shall be smooth and free from tool marks and ridges.”

Even if you have no idea what the standard states, if there are problems with the installation, you have a solid, written standard to rely on to establish whether the product was installed correctly. See list of trade associations that publish standards.

Other published standards.  Some contractors cite a specific minimum quality standard such as the Residential Construction Performance Guidelines, published by the National Association of Homebuilders (NAHB). These standards cover the entire building from foundation to roof, establishing quality standards for everything from foundation cracks to painting quality. Each entry also includes commentary and corrective actions. A couple of examples follow:

Concrete Slabs: Concrete floors in living areas will not have pits, depressions, or areas of unevenness exceeding 3/8 inch in 32 inches. Corrective Measure: The contractor will correct or repair the floor to meet the guideline.

Drywall: Any joints that are visible from a standing position of 6 feet under normal lighting conditions are considered excessive.  Corrective Measure: One time only during the warranty period, the contractor will repair affected areas.

The first standard for concrete slabs is pretty lax in my opinion. It falls well short of the TCNA Standards for ceramic tile, which call for no more than ¼ in. variation in 10 ft., but may be suitable for some types of floor coverings such as thick carpeting.

The second standard seems pretty reasonable to me. However, I would ask for a one-year warranty on the repair in the event that the repair is inadequate, or that the building continues to move and settle after one year – generally not a good sign.

Many of the standards, for example, allowing a ¼ inch gap allowed where cabinets fit to a wall, are pretty lax and would not meet the standards of most custom builders. Although this book is a mixed bag, and was written by a contractors’ organization  primarily to protect contractors from unreasonable claims, at least it does the job of establishing objective measures of quality.

For a homeowner unfamiliar with the nitty-gritty details of construction, the book can provide a good introduction to the many types of quality issues that come into play and can serve as a starting point for establishing minimum quality standards acceptable to both parties. If a particular aspect of the job – for example, the interior woodwork, is of particular importance to you, it may make sense to establish a specific standard, borrowing from the style, if not the specific dimensions, of this book. The book allows 1/8-inch gaps in interior trim – if you are paying premium rates for custom trim, maybe a 1/16-inch gap is more reasonable.

In most cases, the standards established by individual trade organizations for drywall, ceramic tile, hardwood flooring, wood siding, etc.,  are more stringent than in the NAHB Guidelines, so referencing the individual standards would be preferable. If you are using an architect, he is likely to reference industry standards through the Master Spec or a similar spec writing system. Also most custom builders would aim for higher standards in their work due to professional pride, and their desire to satisfy their customers and get repeat work and referrals. That’s the contractor you want to hire.

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