Synthetic vs Felt Underlayment for Michigan Roofs

Every reroof quote in Macomb County has a line for underlayment, and almost nobody asks about it. The conversation jumps straight from shingle color to price. But the material stapled or nailed to your deck before a single shingle goes down is what protects your house during the install itself, and it quietly affects how the finished roof behaves for decades after. This page runs the honest ledger on asphalt felt versus synthetic underlayment: what each one is, how each performs on an actual Michigan job site, and where the real money question sits inside your total reroof cost.

01 /What each material actually is

Asphalt felt, sometimes called tar paper, is the underlayment roofers have used for generations: a fiber mat saturated in asphalt, sold by weight per roll (traditionally 15 pound or 30 pound). It is cheap, familiar, and every roofer knows how to install it. It has also been the underlayment beneath the overwhelming majority of existing roofs across Warren, Sterling Heights, and every other Macomb County city, which is part of why it is still the default a lot of homeowners expect.

Synthetic underlayment is a woven or spun polymer sheet, usually polypropylene, with a coated top surface for grip and water resistance. It is newer to the market, sold by square footage covered rather than weight, and a single roll typically covers several times the area of a felt roll, which means fewer rolls carried up a ladder and fewer seams on the finished deck. Both materials do the same basic job: a secondary water barrier under the shingles and over the deck. How well each one does that job, and how each one behaves in the days before the shingles go on, is where they actually diverge.

02 /How they perform once the crew is on the roof

The biggest practical difference shows up during the install itself, not years later. A Macomb County reroof can get rained out mid-job, especially in spring and fall, and a partially covered deck sitting exposed overnight is a real risk either way. Felt absorbs moisture, and once it gets wet it can wrinkle and buckle, which telegraphs through the shingles above it and can trap moisture against the deck. Synthetic sheds water and generally lies flat even after a surprise shower, which is one reason more crews reach for it on jobs with any weather risk in the forecast.

Wind is the other job-site factor. An exposed deck between tear off and shingle install is vulnerable, and felt has a lower tear strength: a gust can lift and tear a corner before it is fastened down or covered. Synthetic sheets are engineered with a tighter weave and higher tear resistance, so they tend to survive a windy afternoon on the roof better than felt does. Neither material is doing its permanent job yet at that stage; this is purely about surviving the install.

03 /What neither one replaces: ice and water shield

This is the point where the underlayment conversation gets confused, so it is worth saying plainly: neither felt nor synthetic underlayment is ice and water shield, and neither one replaces it. Ice and water shield is a self-adhered rubberized asphalt membrane, a different product entirely, installed at eaves, valleys, and roof penetrations where Michigan's freeze and thaw cycle does the most damage. Underlayment covers the rest of the deck; ice and water shield covers the vulnerable edges and low points where meltwater backs up under normal shingles.

Michigan's building code addresses this as a separate, mandatory requirement, not an optional upgrade (see Michigan Residential Code 2015, section R905.1.2 (ice barriers)), calling for a self-adhered ice barrier membrane at eaves in the climate zones that cover Macomb County. That code line exists because of exactly the ice dam problem this county sees most winters: heat escaping a poorly ventilated attic melts snow, the meltwater refreezes at the cold eave, and it backs up under anything that is not sealed and adhered. Choosing synthetic over felt for the field of your roof does not change what your eaves and valleys need. Both materials get paired with proper ice and water shield on a correctly built Michigan roof.

04 /The cost impact inside a Macomb County reroof

Underlayment is not priced as its own service; it is a line item inside a full roof replacement, and in Macomb County a typical asphalt shingle replacement runs $9,000 to $18,000, with most homes landing between $12,000 and $16,000. Full pricing detail lives on our pricing sheet, and you can run your own numbers on the 60-second cost calculator. Synthetic typically adds a modest amount to that total compared to felt, since the material itself costs more per square even though fewer rolls are needed to cover the same deck.

In other words, the felt versus synthetic decision rarely moves your quote into a different price bracket. It is a small percentage swing inside the same reroof, which is exactly why it is worth deciding on performance rather than on shaving a few dollars off an already-competitive line item. Our underlayment cost guide breaks down where that line sits inside a real Macomb County quote in more detail.

05 /How to decide

For a small, contained repair where the existing deck is already covered in felt and only a section needs patching, matching felt is a defensible, practical call; there is little upside to introducing a different material for a repair that small. For any full tear off and replacement, synthetic is the sounder default in this climate: better tear resistance while the deck sits exposed, no wrinkling if a spring storm catches the job mid-install, and a small material cost difference that does not change which price bracket your reroof lands in. Whichever underlayment goes down, make sure ice and water shield is specified separately at the eaves and valleys, since that is the layer actually built for Michigan's ice dam physics.

If you want the fuller picture before your reroof, our tear off vs overlay comparison covers the bigger decision synthetic and felt both live inside, and ridge vent vs box vents looks at the ventilation half of the same ice dam story. Or skip the reading: a free inspection gets you a written quote that spells out exactly which underlayment and which ice and water shield are specified, line by line.