Hafsteinn Gunnar Sigurðsson was browsing in a local store in his native Iceland when he just had to stop and chuckle. For the past few years, he had been working on a script with Huldar Breiðfjörð about escalating dispute between a pair of neighbors in Iceland and while the film unfolds along the lines of a classic thriller, he was tickled when he came across one particular ceramic figurine pulling his pants down and knew it had to go in his next film.

“We had gnomes already in the script and then I saw this dirty version in a store in Iceland and they just called to me,” laughs Sigurðsson, whose mischievous humor is laced throughout the pitch-black comedy “Under the Tree.”

It isn’t the only scene in which someone shows their ass in the latest from the devious writer/director, which begins with embarrassment when a man named Atli (Steinþór Hróar Steinþórsson) is thrown out of the house by his wife Agnes (Lára Jóhanna Jónsdóttir) after being caught watching a sex tape involving a former lover Rakel (Dóra Jóhannsdóttir) and sees things only go downhill from there when he goes to live with his parents Baldvin (Sigurður Sigurjónsson) and Inga (Edda Björgvinsdóttir) in the suburbs. While Atli appears to have it made in the shade in their quiet neighborhood, the old oak sitting in his parents’ backyard casts a more ominous shadow over the house, upsetting the couple next door, Konrad (Þorsteinn Bachmann) and his wife Eybjorg (Selma Björnsdóttir), who likes to sunbathe, who urge Baldvin and Inga to trim the tree back. A war of words between the couples gives way to increasingly nastier displays of protest, paralleling the increasingly ugly battle Atli and Agnes have over the custody of their young daughter, and although Sigurðsson has plenty of fun figuring out ways in which all involved attempt to outmanuever one another, “Under the Tree” cuts even deeper than its sharp humor when observing the thorny relationship dynamics between the married couples as they decide what the best way forward is, often at odds with other as much as who’s on the other side of the fence.

Sigurðsson may not be well-known in the States, though his feature debut may be — the 2011 charmer “Either Way” was the inspiration for David Gordon Green’s “Prince Avalanche” — but if there’s any justice, “Under the Tree” should change that and following the crowdpleaser’s rampage through the fall festival circuit last year, Sigurðsson spoke on the eve of the film’s release in America about balancing the comedy and drama in his latest film, how the scarcity of trees can bring out the passion of the traditionally polite society in Iceland and how he meticulously lays the plans for a smooth shoot.

Sigurður Sigurjónsson in "Under the Tree"How did this come about?

This idea had been brewing for quite a few years, which I started talking about with my co-writer. We have a lot of true cases in Iceland [of these] neighborly conflicts that revolve around trees and it’s quite nasty and often brutal cases that can spiral out of control. We don’t have a lot of trees [in Iceland], so people who have big, beautiful trees get emotionally attached to them and at the same time, the summers are very short and the sun doesn’t come out that much, so if you don’t have sun hitting your [yard], then you’re going to do everything you can to make sure you do that. But usually the key players in these stories are normal, respectable people who are really not known for aggression or violence, so that [contrast] was the original inspiration, and then this really developed into its own fictional story.

Was there anything important about the area that you’d set this in culturally or geographically?

I wanted to find this peaceful and normal [neighborhood] where people live quite uneventful lives where aggression and violence is very far away. [The housing in the film was] actually one of my favorite architects in Iceland. He built a lot of nice stuff in the ‘50s and ‘60s, so it’s like an old suburban neighborhood in Reykjavík and the shapes and the forms and the squares really help give you that feeling of peace and tranquility. Also, [there’s] that blue color because we have a lot of white houses in Iceland and when Monika [Lenczewska], the cinematographer, and I started discussing this and I presented her with this location, she just totally fell in love with the blue, which I also liked a lot. It really helped because we were shooting quite a lot in the sun and if you’re shooting on a white background, that really burns out the highlights, so it’s very problematic, but that blue color just swallows the light, so it worked from both an aesthetic and practical standpoint.

Steinþór Hróar Steinþórsson in "Under the Tree"There may not be anything to it, but it was always really interesting when you’d shoot behind glass, particularly when there’s a scene between Atli and his old lover Rakel. Was that something you kept an eye out for?

That’s part intuition and that was just something that we found on that location, these reflections. There’s a layer of the past in there, so I think you can interpret it in many ways that work dramatically for the scene, but also that are visually pleasing.

I understand you bring in Monika as early as rehearsals. Does that give a feeling to how you’ll frame the characters later in a shot?

It just makes the process much more natural somehow, more organic because you know it starts with me and Monika sitting around a table, designing all the shots. That may often change when you actually have the actors in the location, blocking and figuring out how the scene works best inside that specific location, but it’s something I’ve developed on my previous films is to spend the last week [of prep] on location with the actors and the cinematographer to make all these big creative decisions before you get the whole circus — the whole crew and the lights and everything on the day of shooting because then it’s hard to have space to make decisions. If you do it beforehand, then you figure out a plan, which can often change, but you can really maximize the time you have with the crew and everybody to get the best shots and the best performance out of the actors.

Sigurður Sigurjónsson and Þorsteinn Bachmann in "Under the Tree"In general, you’re said to spend a lot of time with your actors before shooting. How full formed are the characters on the page versus what you may want to incorporate from your time with them?

They’re quite developed on the page, but I want a creative relationship with my actors, so during my process usually when we start out, I really try to create an environment where all ideas are welcome, to encourage people to participate and throw in ideas. Then it’s my job as a director to work out what works for the story and what doesn’t. It’s part of the job I like a lot and I put a lot of emphasis on, which is preparing with the actors.

I realized that on a script level that I wanted to approach the story partly as a thriller, although it might not be that obvious when you read the script, but because the script has a lot of comedic elements, I [also] chose to cast actors that had these comedic elements to them, so I wouldn’t have to push for it. It would just come through in a way that’s not forced, and it was interesting for me, and also I think for audiences, who know these actors from totally different things, than they do in this film.

Was making a film with those genre elements exciting from a technical standpoint? You do your spin on a car chase, for example.

Yeah, that was kind of a guerrilla-style thing that we were doing. The last scene of the movie, which I don’t want to spoil, but where things escalate out of control, was also a challenge. I had never done a scene like that before, so a lot of that was new to me, which I had to learn, but what’s great about film is that each film has a different set of tasks or problems that you have to figure out. Experience can teach you a lot, but there are always new problems to each film.

Selma Björnsdóttir in "Under the Tree"Is it true that the tree had to be added in post-production?

Yeah, that’s a good example of one of these problems nobody had encountered before, so we had to invent the wheel a little bit. We had to be very organized in all our shots that included the tree because we had the trunk [of the tree] on location, but we had to insert the crown in post, so we had to storyboard all the scenes in the garden. That was definitely a challenge.

Since this is such a crowd pleaser, what’s it been like taking this around the world and seeing the different reactions to it?

It’s been a lot of fun. It certainly causes a lot of different reactions. A lot of people find it hilariously funny while other people experience it as a heavy drama, so it really splits people. But that’s what I really like about it, that it’s hard to calculate. The reception here in the States has been good so far and in filmmaking, you’re always working in the dark. In the editing and in the writing, you’re guessing all the time, and you never really know what you have until you see the film with an audience, how they respond and react, so that’s a really big part of the learning process for me.

“Under the Tree” opens on July 6th in Los Angeles at the Laemmle Royal, Miami at the Miami Dade College Tower Theater and New York at the Quad Cinemas. A full list of theaters and dates is here.